Substantial Modification

The concept of substantial modification sits at the heart of European contract modification law. It is the dividing line between a lawful amendment to an existing contract and an unlawful award of a new contract without competition. Getting this distinction wrong exposes contracting authorities to ineffectiveness proceedings and leaves incumbent suppliers holding contracts that may be legally challenged by competitors who should have had the opportunity to bid.

What is a substantial modification?

Article 72(4) of Directive 2014/24/EU defines a modification as substantial if it renders the contract materially different in character from the one originally concluded. The Directive specifies four concrete tests for substantiality. A modification is substantial if it introduces conditions which, had they been part of the original procurement, would have attracted additional participants, allowed different tenderers to be selected, or allowed the winning tenderer to be selected; if it changes the economic balance of the contract in favour of the contractor in a way not provided for in the original contract; if it considerably extends the scope of the contract; or if a change of contractor takes place other than in the circumstances permitted by Article 72(1)(d).

These tests are applied cumulatively and in context. A price increase of 5% on a small contract might not be substantial. A restructuring of the payment mechanism that fundamentally shifts financial risk from contractor to authority is likely to be substantial even if the headline price is unchanged. The Court of Justice of the EU has consistently interpreted "substantial" broadly, reflecting the competition-protection purpose of the rules.

The modification threshold (10%/15% rule) provides a safe harbour for value-based changes below those percentages, but even sub-threshold changes can be substantial if they meet the qualitative tests above. Threshold compliance does not automatically immunise a modification from substantiality review.

In the UK, the Procurement Act 2023 adopts a similar framework. Modifications that would have changed who won the original competition, or that give the contractor a material advantage not anticipated in the contract, are treated as substantial and require a new procurement.

Why it matters for bidders

If a contracting authority makes a substantial modification to a contract held by a competitor, you as a market participant may have grounds to challenge the modification. Competitors who were not selected in the original procurement but would have bid differently (or would have won) had the modified scope been advertised can bring review proceedings. Monitoring modification notice publications in TED and Find a Tender is therefore a legitimate competitive intelligence activity.

Conversely, if you are the incumbent and your client proposes a change that might be substantial, understanding this framework allows you to advise your client honestly about their obligations, reducing the risk that a well-intentioned amendment creates legal exposure.

Example

An Austrian federal agency awards a five-year IT systems contract. Eighteen months in, it proposes to add a cloud migration workstream worth 45% of the original contract value. That addition is not covered by any review clause, was not foreseeable, and exceeds the de minimis modification threshold. It almost certainly constitutes a substantial modification, requiring a new procurement or, at minimum, a careful legal assessment.

Frequently Asked Questions

Can a modification be both below the financial threshold and still be substantial?

Yes. The financial threshold (10% for services and supplies, 15% for works) prevents a below-threshold change from being caught solely on value grounds, but a change can still be substantial on qualitative grounds. A modification that restructures the contract's core purpose, even at low cost, may be substantial.

Who decides whether a modification is substantial?

Primarily the contracting authority, with legal advice. But that assessment is subject to challenge before national review bodies (for example, the UK's High Court or equivalent national procurement tribunals in EU member states) and ultimately before the Court of Justice of the EU through preliminary reference.

Is there a safe way to make substantial changes without a new procedure?

Generally no, unless the contract documents included a review clause or option that covers the proposed change. That is precisely why including well-drafted review clauses and options at the outset is so important. Changes that fall within a pre-published clause are non-substantial modifications by definition.