I have tried throughout my time writing on London housing policy to be constructively critical of the Mayor and support Mayoral policy where it’s right. On the emergency measures — the Support for Housebuilding London Plan Guidance published in March — he is right. The package is necessary, broadly proportionate, and long overdue. London’s housing starts had fallen to historic lows. The 35% affordable threshold was not delivering affordable housing; it was delivering nothing. The Mayor made a difficult call and I support it.
Which is precisely why what I am now hearing from colleagues is so concerning.
A Legal Challenge Is Coming
At the Hounslow Examination in Public, a King’s Counsel confirmed that multiple London boroughs are considering making a legal challenge to the emergency measures. The consensus among those taking advice is that the period for legal review runs to 19th June — the default three-month window that applies because the LPG was issued under a GLA-related Act rather than the Planning Act.
I also hear chatter that a judicial review application has already been filed by one Borough. Nothing is confirmed publicly at this stage and I will not name names. But the direction of travel is clear, and the grounds being considered are serious enough to warrant open discussion.
The Legal Grounds
Three grounds are in play, and it is worth setting them out plainly.
The first is ultra vires. London Plan Guidance is statutorily constrained to elaborating on adopted policy. The argument being made is that the Support for Housebuilding LPG does not elaborate on H4, H5 and H6 — it materially departs from them, particularly on the affordable housing threshold and the fast-track route. If that is right, the Mayor has used guidance to do what only a Plan review can lawfully do. The fact that the measures are time-limited does not cure this — the argument is the mechanism is wrong regardless of duration or intent.
The second is inconsistency with the development plan. Section 38(6) of the Planning and Compulsory Purchase Act requires decisions to accord with the London Plan unless material considerations indicate otherwise. Boroughs determining applications by reference to the LPG rather than adopted H4/H5/H6 may therefore be vulnerable on appeal, regardless of whether the LPG itself survives challenge. This is arguably the most practically dangerous ground — not because it will necessarily succeed, but because its mere existence creates uncertainty for any developer attempting to use the fast-track route in the window before legal clarity is established. The chilling effect is the point.
The third is procedural. Whether consultation on guidance is sufficient where the substantive effect is a plan amendment, which would require examination by an independent Panel. The GLA’s consultation process should demonstrate this, but the question remains live if the court accepts the first ground.
A Better Legal Route Was Available
This is where I want to offer something constructive rather than simply rehearse the problem.
The GLA could have — and arguably still could — make a stronger case by framing the measures differently. The argument that would sit more comfortably within the existing plan architecture is not that the LPG departs from H5 and H6, but that the evidence base which informed H5 and H6 is now demonstrably out of date.
The data is all there. Housing starts at historic lows. Affordable housing starts in 2024/25 at a fraction of 2022/23 levels. More than a third of boroughs recording zero new home construction starts in a single quarter. A viability crisis acknowledged by almost everyone.
The argument would run: the evidence base underpinning H5 and H6 has been overtaken by events that the plan’s authors could not have anticipated. In that context, and read alongside the strategic housing policies and DF1, H5 is no longer doing what it was intended to do. Applied mechanically, it is actively undermining the plan’s own housing delivery objectives. The LPG is therefore not a departure from adopted policy but a necessary intervention to prevent the plan from being frustrated.
That is a material considerations argument. It sits within Section 38(6). It does not require dressing up a policy change as guidance elaboration. And it is factually unimpeachable.
Whether it is too late to reframe the defence on those lines is a question for the GLA’s legal team. But if a challenge does reach court, this is the ground I would want to be standing on and I would be picking up the phone to Tim Craine who can give a forward look on the sustained collapse over 2026.
The Political Context
The local election results last week make this more urgent, not less. Several boroughs that have now changed hands — or moved into no overall control — are in the hands of parties that are, at best, ambivalent about new development. The Greens have a retrofit-first policy. Reform took Havering on a platform of an 8-storey development ceiling. The Liberal Democrats have rarely been enthusiastic advocates of housing supply.
The turn out looks really low – how much the system has been captured by ideologues and the anti-growth lobby is yet to be determined. But be under no doubt, it is open to capture. Whilst many Londoners work and live busy lives, our politicians like to play at committee and with peoples lives.
If legal challenge becomes the vehicle through which newly emboldened borough administrations resist Mayoral authority on housing, the emergency measures could be neutralised before they have delivered a single additional home. That would be a serious failure — not of the policy, but of the mechanism chosen to deliver it.
The boroughs considering challenge should reflect on what they are actually arguing. They are not defending affordable housing. The 35% threshold was not delivering affordable housing. They are defending a target while opposing the only practical route to delivery. That is a political position dressed up as a legal one, and it deserves to be named as such.
Conclusion
The Mayor is right on the substance. London needs these measures and the window to use them is short — both legally, with the review period running to June, and practically, with the 2028 deadline for the fast-track route already creating time pressure on developers.
The GLA should urgently consider whether its legal position can be strengthened by reframing the evidential case for the measures within the existing plan architecture. And those boroughs taking or contemplating legal action should be honest with themselves and their residents about what a successful challenge would actually mean — not more affordable housing, but less of it.
That should not be a difficult argument to make. But if London is to bounce back, it is a necessary one.
