Contract variations and procurement: a practical guide under the Procurement Act 2023

Contract variations, procurement and UK public sector

Public buyers tend to call them “modifications,” suppliers say “variations.” Either way, changing a live public contract is now more flexible than under the old rules, and far more transparent. This guide explains when a change is possible, what notices to publish, and how to avoid challenge risk. If you want a fuller explainer of the terminology, see our plain English overview of contract amendments.

What changed under the Act

The Act sets clear routes for changing a contract. The ones you will see most often are non-substantial changes, below-threshold changes, options that were clearly provided for in the original contract and notice, unforeseeable circumstances, materialisation of a known risk, additional goods, services or works, and transfer on corporate restructuring. Some routes cap increases in value, and none allow a change that would alter the overall nature of the contract.

Transparency you should expect

Before most modifications, authorities publish a Contract Change Notice on the central platform. Smaller movements in value or term can be exempt from publication. For higher value contracts, a copy of the modification or the contract as modified may also need to be published. Consider a short voluntary standstill for significant changes to reduce challenge risk.

The common grounds, in plain English

• Non-substantial changes: allowed if scope is not materially changed, the economic balance does not shift in the supplier’s favour, and any change to duration stays within the limits.

• Below-threshold changes: limited movements in value, with aggregation rules and no material change to scope.

• Provided for in the contract: the option to change was unambiguously priced and described in the original contract and notice.

• Unforeseeable circumstances: genuine surprises, usually with a value cap and no change to overall nature.

• Known risk materialises: a specific risk flagged in the original notice bites, and it is better value to amend than to retender.

• Additional goods, services or works: switching supplier would create incompatibility, technical difficulties, significant inconvenience, or duplicated cost.

• Corporate restructuring: novation or assignment after a merger or insolvency, with the usual checks on excluded suppliers.

Frameworks and call offs

The Act’s modification rules apply to frameworks and call offs. If you want to rely on the known risk route, the specific risk must be identified in the framework tender or transparency notice before award. If you want to rely on the provided for route at call off, describe the possible options in the framework notice and build clear change control into the call off terms.

Buyer checklist at framework design:

• State any options that may be exercised later, including pricing method and maximum term or value.

• Identify any known risks that could require a later change and explain why amending would be in the public interest.

• Set out who will publish Contract Change Notices and when.

• Include audit trail requirements and conflicts of interest checks.

• Align call off schedules so the same rules apply in practice.

For a plain English primer on terminology, see our guide to contract amendments.

A buyer’s five quick checks before approving a variation

1. Choose the correct legal ground and record why it fits the facts and the contract.

2. Test scope and economic balance. Confirm there is no material change to what is delivered and no shift in the bargain in the supplier’s favour.

3. Recalculate value and term with aggregation. Include earlier changes and confirm any caps still hold.

4. Prepare transparency. Draft the Contract Change Notice, decide on voluntary standstill, plan any lawful redactions, and schedule publication.

5. Evidence value for money. Use benchmarking, existing pricing mechanisms, or a short market check where appropriate, and record your reasoning.

Contract administration basics for authorities

Put the variation in writing and have it signed in line with the contract’s variation clause. If there is no consideration, use a deed of variation. Keep approvals, conflicts assessments, and impact notes on KPIs, milestones, and payment schedules. Update contract registers and notify finance so funding and reporting stay accurate.

Typical pitfalls for buyers

• Making serial small changes that should be handled as a single modification.

• Relying on known risk when the risk was not identified in the original notice.

• Allowing a change that alters the overall nature of the contract.

• Forgetting that below threshold changes add up against the publication threshold.

• Missing publication for novation after corporate restructuring.

• Not updating framework documentation so call offs cannot lawfully rely on options.

How we help

We support contracting authorities to plan and deliver compliant modifications. This includes drafting framework options that can be exercised later, testing scope and value for money, preparing Contract Change Notices, and setting up a clear approval trail. If you need hands on support across a portfolio, our team delivers end to end procurement consultancy services

Public sector contract variation examples under the Procurement Act 2023

Before you start, confirm which regime applies. If the procurement was commenced before 28 October 2024, use the Public Contracts Regulations 2015 regulation 72. If it commenced on or after 28 October 2024, use the Procurement Act 2023.

1) Short extension to finish mobilisation on a services contract

Situation: You need a three month extension to complete data migration on a services contract.
Legal route: Non-substantial modification. Confirm there is no material change to scope or economic balance and that the time increase is within the limit based on the original maximum term.
Transparency: A Contract Change Notice is usually not required if the term increase is within the publication thresholds. Record your reasoning.

2) Indexation that was priced in from the start

Situation: A multi-year ICT support contract includes a clear price review clause linked to an index and a cap.
Legal route: Provided for in the contract. The option was unambiguously described in the contract and the original notice, so exercising it is permitted.
Transparency: Often no Contract Change Notice is needed because value and term were already within the original maximums. Keep the audit trail.

3) Additional software module that must integrate with the incumbent platform

Situation: You need an extra module from the same vendor and switching supplier would create incompatibility and duplicated costs.
Legal route: Additional goods, services or works, with the usual cap and no change to overall nature.
Transparency: Publish a Contract Change Notice and explain why the compatibility test is met. Consider a short voluntary standstill on significant changes.

4) Known cyber risk materialises on a call off

Situation: A council discovers new security vulnerabilities affecting a software as a service call off under a framework.
Legal route: Materialisation of a known risk, but only if that specific risk was identified in the framework tender or transparency notice before award. If it was not, consider another ground or a new procurement.
Transparency: Prepare a Contract Change Notice that sets out the risk and why amendment is in the public interest.

5) Corporate restructuring of the supplier

Situation: Your waste collection contractor transfers the business to a new group company following a merger.
Legal route: Transfer on corporate restructuring, provided the new supplier is not excluded.
Transparency: You must publish a Contract Change Notice for novation, even if the change is otherwise below the publication thresholds, and complete a conflicts assessment.

6) Small value tweak to a works contract

Situation: Minor extra civils works on a highways job worth a small percentage of the current contract value.
Legal route: Below-threshold modification, provided there is no material scope change and aggregated below-threshold changes stay within the thresholds.
Transparency: Usually no Contract Change Notice, but keep cumulative calculations on file.

7) Convertible contract that steps over the threshold

Situation: A below-threshold building maintenance contract needs an uplift that would take it over the public contract threshold.
Legal route: Convertible contract. Treat it as a public contract for modification purposes and proceed only if a permitted route applies.
Transparency: Publish a Contract Change Notice and follow the publication rules for qualifying modifications where applicable.

8) Urgency to protect life

Situation: Flood response requires rapid augmentation of an existing equipment contract to protect life and property.
Legal route: Urgency and protection of life. Use this only where the purpose could alternatively be achieved by a direct award under emergency routes, and keep justification tight.
Transparency: Publish a Contract Change Notice and record why this ground was necessary.

What to publish and when

Before most modifications you publish a Contract Change Notice on the central platform, including the ground used, the change to value or term, key dates, and whether a voluntary standstill applies. For qualifying high-value changes, publish the modification or the contract as modified within the deadline.

FAQs for public sector buyers

Can I rely on “non-substantial” for a short extension if the contract has already been extended once?
Yes, if the total increase in duration stays within the limit based on the original maximum term and you do not materially change scope or the economic balance. If not, check below-threshold or a Schedule 8 route.

Do below-threshold changes need a notice?
Often no, provided the change stays within the percentage limits and there is no material change to scope. Keep a running total, since multiple small changes can push you over thresholds.

Can I use the 50% cap more than once under unforeseeable circumstances or additional needs?
You can rely on a permitted ground again if the facts support it, but the cap applies each time against the contract’s estimated value at the point of change. Repeated use attracts scrutiny, so document your reasoning and value-for-money position.

What if a known risk was not flagged in the original notice?
You cannot use the “known risk” ground unless the specific risk was identified before award. Consider other grounds, or retender if the change would alter the overall nature.

Do light touch and below-threshold contracts follow the same rules?
Light touch and below-threshold contracts have more flexibility. You can usually change them without fitting a specific ground, but transparency and good record-keeping still apply.

When must I publish the modified contract, not just the notice?
When a qualifying modification takes a public contract over the publication threshold, you must publish the modification or the contract as modified within the time limit. Redact only where the Act allows.

Do I need a voluntary standstill for modifications?
Not mandatory. It is good practice for significant changes because it reduces the risk of a court setting the modification aside. Use a short, clearly signposted period.

How do frameworks and call-offs work for “provided for” options?
If you want to rely on options at call-off level, the framework notice must describe them with enough detail. If it did not, consider other grounds or run a fresh competition.

Can I combine a permitted change with something that is not permitted?
No. The Act prevents packaging a non-permitted modification with a permitted one. Handle them separately, or retender the non-permitted element.

What records should I keep on file?
Keep the business case, ground chosen, value calculations including aggregation, scope analysis, conflicts assessment where relevant, the Contract Change Notice, and any standstill correspondence. This evidences compliance and supports future audits.

If you need a quick sense-check on a live change or want us to draft the paperwork, call 01204 238046 or email hello@thorntonandlowe.com.