Unilateral undertaking against a bilateral section 106 deed
Both instruments are made under section 106 and both bind the land. The difference is that a unilateral undertaking cannot contain any obligation on the authority.
A unilateral undertaking is a planning obligation given by the landowner alone. A bilateral deed is an agreement between the landowner and the local planning authority, and usually any other authority with an interest. Both are made under section 106 of the Town and Country Planning Act 1990, both bind the land and both are registered as a local land charge. The unilateral undertaking vs section 106 agreement choice usually comes down to whether the authority will engage, and the single structural difference is that nobody can give a covenant to themselves.
That difference has one large consequence. A unilateral undertaking cannot contain any obligation on the authority, so it cannot commit the council to spend a contribution on anything, to return unspent money, or to limit its monitoring fee.
Who the parties are in each
A bilateral deed is executed by the landowner, by anyone else with an interest the authority wants bound, by any mortgagee that is prepared to be a party, and by the authority. On a scheme with a county council handling education and highways in a two-tier area, both authorities are parties.
A unilateral undertaking is executed by the landowner and anyone else with an interest. The authority does not sign. The instrument has to identify the local planning authority against which it is enforceable, because section 106 makes an obligation enforceable by the authority identified in the instrument.
Who must be a party is a title question rather than a planning one. Freeholder, any leaseholder with an interest capable of being affected, and any option holder or contract purchaser whose interest would otherwise escape the obligation. An obligation that misses an interest is an obligation with a hole in it, and the authority's legal team will find it.
| Feature | Unilateral undertaking | Bilateral deed |
|---|---|---|
| Authority a party | No | Yes |
| Obligations on the authority | Not possible | Possible |
| Negotiation required | None, in principle | Yes |
| Timescale | Controlled by the applicant | Controlled by the authority's legal team |
| Authority's legal costs | Usually not recoverable | Normally paid by the applicant |
| Typical use | Appeals, uncooperative authority | Most grants of permission |
When a unilateral undertaking is the only option
Three situations, and the first is by far the most common.
At appeal, where the authority has refused permission and has no reason to help you complete a deed on an appeal it is defending. The Planning Inspectorate needs a completed obligation and the authority has no incentive to engage, so the undertaking is the practical route.
Where the authority's legal team cannot complete in the time available. A resolution to grant subject to a section 106 agreement can sit for months, and where a funding or option deadline is approaching, offering a unilateral undertaking that delivers the same obligations sometimes unlocks it.
Where the only obligations are negative or financial and need nothing from the authority. A restriction on occupation, a financial contribution with a payment trigger, or a covenant not to use a building for a specified purpose can all be delivered unilaterally without loss.
Where the scheme needs the authority to do something, the undertaking route fails. Transfer of land to the council, adoption of open space, nomination rights over affordable units, a cap on a monitoring fee or an agreed mechanism for returning unspent contributions all require the authority's covenant, which means a deed.
Enforceability and the authority's position
A properly executed unilateral undertaking is as enforceable as a deed. Section 106 makes a planning obligation enforceable against the person entering into it and against anyone deriving title from them, and the authority can enforce a financial obligation as a debt and seek an injunction to restrain a breach of a restriction.
Authorities nevertheless dislike them, for reasons worth understanding rather than dismissing. An undertaking drafted by the applicant uses the applicant's wording, and triggers, definitions and payment mechanisms drafted by one side tend to favour that side. Authorities also lose the ability to recover their legal costs, which on a complex obligation is a real sum.
The practical answer is to draft an undertaking using the authority's own model wherever one exists. Most authorities publish a model section 106 template, and an undertaking built on that template, with the authority's own definitions and payment mechanisms, is far more likely to be accepted without argument.
Use at appeal and the Inspectorate's expectations
The Inspectorate expects a completed, dated and executed obligation by the deadline set in the appeal timetable, and an obligation arriving late or in draft may be given no weight. That is the single most common way a good appeal case is undermined.
Three practical points.
- Submit a draft with the appeal statement and the executed version by the stated date. The inspector can then raise drafting points while there is still time to fix them.
- Address the obligation tests expressly. Regulation 122 of the Community Infrastructure Levy Regulations 2010 requires each obligation to be necessary to make the development acceptable in planning terms, directly related to the development, and fairly and reasonably related in scale and kind. Set out the justification for each obligation in the Planning Statement or in a short separate note, obligation by obligation.
- Where the authority and the appellant disagree about what is needed, offer the obligations in the alternative, so the inspector can accept some and not others. An all-or-nothing undertaking forces a choice that may go against you.
Where the appeal concerns affordable housing, the tenure and transfer mechanism have to be workable without the authority's covenant, which usually means an obligation not to occupy market units until the affordable units are transferred to a registered provider on stated terms. The supporting case belongs in an Affordable Housing Statement, with the appraisal in a Viability Assessment where the offer is below policy.
Mortgagee exclusion and title issues
Any obligation needs a title check before drafting, not after. Order an official copy of the register and the title plan, confirm the extent of the application site against the title extent, and identify every charge and every noted interest.
A mortgagee exclusion clause provides that the lender is not bound by the positive obligations while it holds only a charge, and becomes bound if it takes possession and develops. Authorities accept that. What they resist, reasonably, is an exclusion wide enough to let a receiver sell the site free of the obligation altogether.
Two traps. A unilateral undertaking given by a landowner whose land is charged, without the chargee joining or an acceptable exclusion, may be worth less than it appears on an enforcement. And where the site is unregistered or the title extent does not match the red line, the obligation may not bind the land you think it binds. Both are solicitor's work and both take longer than anyone allows.
Variation and discharge of each
Section 106A governs modification and discharge. An obligation may be modified or discharged by agreement between the authority and the person against whom it is enforceable, which means a deed of variation and the authority's consent in both cases.
The alternative route opens after five years from the date the obligation was entered into, when an application may be made to the authority to modify or discharge it on the ground that it no longer serves a useful purpose, or serves it equally well in a modified form. A refusal can be appealed to the Secretary of State under section 106B.
So the asymmetry is at the creation stage rather than the variation stage. You can give an undertaking without the authority. You cannot take it back without them.
Choosing the instrument for a specific case
Work through four questions.
Does any obligation require the authority to do, pay, transfer or refrain from something? If yes, you need a deed.
Is there a resolution to grant, and is the authority's legal team engaging within your programme? If yes, a deed is normally better, because the authority's own wording reduces later argument.
Is this an appeal? If yes, plan for a unilateral undertaking from the outset, built on the authority's model, with the regulation 122 justification written alongside it.
Does the title support it? Check before drafting, because the answer sometimes changes the planning strategy.
Where the choice also depends on whether the application will reach committee or be decided under delegated powers, the timetable differs, and committee determination or delegated decision sets out how that affects the programme.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Is a unilateral undertaking as enforceable as a section 106 agreement?
Yes, when properly executed. Section 106 makes an obligation enforceable against the person entering into it and anyone deriving title from them, and the authority can recover a financial obligation as a debt or seek an injunction against a breach of a restriction. The instrument must identify the local planning authority against which it is enforceable.
What cannot go in a unilateral undertaking?
Anything requiring the authority to act. That rules out land transfer to the council, adoption of open space, nomination rights over affordable units, a cap on monitoring fees and any mechanism for returning unspent contributions. Nobody can give a covenant to themselves, so an obligation needing the authority's promise has to be a bilateral deed.
Why do unilateral undertakings get used at appeal?
Because the authority has refused permission and has no incentive to complete a deed on an appeal it is defending, while the Inspectorate still needs a completed obligation. The undertaking lets the appellant deliver the obligations without the authority's signature. Build it on the authority's own model template to reduce drafting objections.
When must an obligation reach the Planning Inspectorate?
By the deadline in the appeal timetable, completed, dated and executed. An obligation arriving late or only in draft may be given no weight, which is a common way a strong appeal case is undermined. Submit a draft with the appeal statement so the inspector can raise drafting points while there is still time.
Can a unilateral undertaking be varied later?
Only with the authority. Section 106A allows modification or discharge by agreement between the authority and the person against whom the obligation is enforceable, which means a deed of variation either way. After five years an application may be made to modify or discharge on the ground that the obligation no longer serves a useful purpose, with an appeal under section 106B.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.