Unilateral undertakings: when they work and when they fail
A unilateral section 106 deed works for self-executing one-way promises. It fails where the obligation needs the authority to covenant, or where the triggers cannot be observed.
A unilateral undertaking is a planning obligation under section 106 of the Town and Country Planning Act 1990 entered into by the person with an interest in the land, without the local planning authority as a party. It works well for a straightforward one-way promise: pay a contribution, provide the affordable units, restrict occupation. It fails where the obligation needs the authority to do something, where the mortgagee will not consent without a clause that guts it, or where the drafting leaves a trigger that nobody can enforce.
Inspectors see a lot of them, and the ones that fail usually fail on drafting rather than on principle.
What a unilateral undertaking is
Section 106 allows a planning obligation to be created either by agreement between the authority and the landowner or by a unilateral deed given by the landowner alone. Both bind the land, both are enforceable by the authority against the person entering into them and against successors in title, and both are registrable as local land charges.
The practical difference is that nobody from the council has negotiated the words. There is no authority covenant, no agreed definition of terms, no monitoring mechanism the council has signed up to, and no opportunity to fix an ambiguity by discussion before execution.
Everything else is the same. The obligation still has to satisfy the statutory tests in the Community Infrastructure Levy Regulations 2010: necessary to make the development acceptable in planning terms, directly related to the development, and fairly and reasonably related in scale and kind. A unilateral undertaking offering something the development does not need is given no weight, and an inspector will say so in a sentence.
Why appellants use them
Three situations account for most of them.
The first is an appeal where the authority has refused and will not engage in drafting a bilateral agreement during the appeal period. The appellant needs the obligation in place before the inquiry or the written representations deadline, so it goes in unilaterally.
The second is a refusal that the appellant thinks can be cured by an obligation the authority never asked for, such as a car-free restriction, a restriction on occupation, or a contribution that answers a specific reason for refusal.
The third is a scheme where there is simply no time. Appeal deadlines are fixed, and the Planning Inspectorate wants a completed, executed deed rather than a draft by the stated date. A unilateral undertaking is the only instrument the appellant controls end to end.
| Factor | Bilateral agreement | Unilateral undertaking |
|---|---|---|
| Authority is a party | Yes | No |
| Authority covenants (to spend, to approve, to repay) | Possible | Not possible |
| Monitoring and administration fee | Usually included | Cannot be agreed |
| Drafting negotiated | Yes | No |
| Timescale controlled by appellant | No | Yes |
| Risk of unworkable triggers | Lower | Higher |
Where the authority refuses to engage
This is common and not always obstruction. A refusal is a decision, and some authorities take the view that negotiating obligations on a scheme they have refused is not a use of officer time until the inspector has decided the principle.
The practical response is to write to the authority early in the appeal period, enclosing the draft, asking for comments by a stated date, and recording that you will execute unilaterally if none arrive. Then do exactly that. Inspectors read the correspondence, and an appellant who tried to agree the words is in a better position than one who did not.
Where the authority does comment, take the comments. A unilateral undertaking amended to reflect the authority's drafting points, even without its signature, is close to a bilateral agreement in substance and attracts the weight that goes with it.
Drafting around an unwilling authority
The craft is in the triggers. Every obligation needs a defined event, a defined obligation, and a mechanism that works without the authority having to agree anything.
Things that work in a unilateral deed:
- A contribution payable on a self-executing trigger, such as before first occupation, with a defined index for inflation and a defined payee.
- A restriction on occupation, defined by reference to a plan and to objective criteria.
- Affordable housing delivery, where the tenure, mix, unit identification and cascade are fully defined in the deed and the schedules, rather than left to later approval.
- A car-free or permit-free restriction, which binds the occupier through a covenant and, in London, through the borough's separate permit controls.
- A phasing restriction preventing occupation beyond a stated number until a defined work is complete.
Things that do not work: anything requiring the council to approve a scheme of works, to enter into a deed of variation, to repay an unspent contribution, to nominate tenants, or to exercise a discretion. Each of those needs the authority to covenant, and it cannot covenant in a deed it has not signed.
Where affordable housing is involved, the registered provider usually needs to be a party or to be accommodated by a cascade, and the mortgagee in possession clauses they require have to be in the deed from the start. The appraisal inputs behind those units should be consistent with whatever was argued on viability, and an independent review of a viability appraisal at appeal will test exactly that consistency.
Monitoring, enforcement and the mortgagee problem
The authority can enforce a planning obligation by injunction, or by entering the land, carrying out the work and recovering the cost. Those powers exist whether or not it signed the deed.
What it will not have is a monitoring regime. Nobody is being paid to track the triggers, nobody has agreed a reporting obligation, and in practice a unilateral undertaking with a contribution payable on an event the authority cannot observe may go unenforced for years. That is a weakness even when it is working in your favour, because an unperformed obligation sits on the title.
The mortgagee exclusion clause is the other structural weakness. Lenders require that the obligation does not bind a mortgagee in possession or a receiver, so that the security is not devalued. Authorities dislike it because it means the obligation disappears precisely when the development is in difficulty. A clause drafted too widely gives an inspector a reason to discount the obligation. Keep it to the narrow commercial requirement and say in the appeal statement why it is limited.
Title mechanics matter too. Every person with a material interest should execute, including long leaseholders and option holders where their interest could defeat the obligation, and the deed should be submitted to the Land Registry for registration as a local land charge. A deed executed by a company that does not own the land is worth nothing.
When a bilateral agreement is unavoidable
Accept this early and plan the programme around it. A bilateral agreement is necessary where the obligation requires the authority to covenant, where a highway agreement under the Highways Act 1980 has to sit alongside it, where a registered provider needs rights the authority must grant, or where the obligation will need varying later and you want an agreed mechanism rather than the statutory route.
It is also better where the scheme is substantial. An Affordable Housing Statement on a major application will usually be underpinned by an agreement with schedules, and the same is true where a Viability Assessment has produced a review mechanism, because a late-stage review needs the authority to receive, assess and respond to figures.
One honest caveat. The weight an inspector gives a unilateral undertaking varies, and the reported outcomes are indicative of how inspectors have approached the question rather than binding. The pattern is that a deed which is clear, self-executing, tested against the regulatory tests and accompanied by evidence that the authority was offered the chance to comment tends to be accepted. One that is vague about triggers, or that asks the authority to do something, tends to be given little or no weight. The same discipline applies to the cost evidence sitting behind it, which is why highway works costs in a development appraisal should be settled before the deed is drafted rather than after.
If you are assembling an appeal pack and want structured first drafts of the supporting documents alongside the deed, see PlanScope pricing for the free report, pay per report and Professional options.
This is general guidance, not legal advice. Planning obligations should be drafted by a solicitor, and the position should be checked with your local planning authority or a qualified professional before you rely 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 good as a section 106 agreement?
It binds the land and is enforceable in the same way, but it cannot contain authority covenants, an agreed monitoring regime or negotiated definitions. For a self-executing one-way obligation it is close to equivalent. Where the obligation needs the council to approve, repay, nominate or exercise a discretion, it cannot do the job.
Does it still have to meet the statutory tests?
Yes. The obligation must be necessary to make the development acceptable in planning terms, directly related to the development, and fairly and reasonably related in scale and kind. An undertaking offering something the scheme does not need carries no weight, and offering more than is necessary does not improve the planning balance.
When does the deed have to be completed for an appeal?
By the date the Planning Inspectorate sets, and it wants a completed and executed deed rather than a draft. That deadline is the main practical reason appellants use the unilateral route, because it is the only instrument whose timetable they control from start to finish.
Why do mortgagee exclusion clauses cause problems?
Lenders require that the obligation does not bind a mortgagee in possession or a receiver, so the security is not devalued. Authorities object because the obligation then falls away at the point the development is in trouble. A widely drafted clause gives an inspector grounds to discount the obligation, so keep it to the narrow commercial requirement.
Who has to sign the deed?
Everyone with a material interest in the land whose interest could otherwise defeat the obligation, including long leaseholders and, depending on the terms, option holders. Submit it for registration as a local land charge. A deed executed by a company that does not hold the land is worthless, and this is checked.
Will the council actually enforce a unilateral undertaking?
It has the power to, by injunction or by carrying out works and recovering the cost, but it has no agreed monitoring regime and nobody is funded to track the triggers. In practice obligations triggered by events the authority cannot observe can go unperformed for years, which leaves an unresolved charge on the title.
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.