Ancient Foundations & the Custom of London: Hidden Loophole or Legal Headache?

In the heart of London, beneath layers of modern planning law and development frameworks, lies an often-overlooked legal relic: The Custom of London, specifically its principle of Ancient Foundations.

For property developers working in or around the Square Mile or even those eyeing historically dense sites elsewhere understanding this Custom could mean the difference between a smooth planning process and an unexpected legal obstacle.

What Is the “Custom of London”?

In essence, the Custom of London is a historic legal principle allowing freehold (not leasehold) owners to rebuild on the same footprint as a former building, to any height, without being liable for interference with neighbouring rights of light.

Under certain conditions, you can develop upward regardless of light loss to adjacent properties—a rare breath of fresh air from standard planning constraints.

But as always, there is a catch.

To rely on this Custom:

• The new structure must sit on the same footprint as the former one (those elusive “Ancient Foundations”).
• You must be a freehold owner.
• The building footprint must be verifiably historic and have had continuous and uninterrupted enjoyment of light (no physical obstructions).
• It applies even if the dominant and servient properties were once under common ownership—unlike general law, where that would reset the 20-year prescription clock.

First acknowledged in Perry v Eames, the Custom has been held to apply not just to houses but also commercial premises, such as the former Bankruptcy Court on Basinghall Street.

Ancient Foundations: Preservation of Rights Beyond Bricks and Mortar

The principle of Ancient Foundations supports the idea that rights of light—and other easements—attach to the site, not the structure. That means:

• Even if a building is demolished and rebuilt, its rights can survive, as long as the new build sits within the old footprint.
• Developers cannot dismiss existing rights of light just because a building is “new”.

This nuance makes historic or reconstructed sites uniquely sensitive to light rights—affecting scale, positioning, and ultimately, project viability.

In practice, the Custom is rarely invoked—but where it can be, it offers:

• Greater design freedom (especially vertically)
• Reduced exposure to rights-of-light disputes
• Faster progression through legal hurdles

Conversely, if you’re building next to a site that might claim rights under Ancient Foundations, you could face costly redesigns, mitigation negotiations, or compensation demands.

Strategic Takeaways for Developers:

1. Due Diligence is Everything
   Investigate past structures and site ownership. If a neighbour can claim Ancient Foundations, you may need to adjust your scheme.
2. Freehold Advantage
   If you’re developing a freehold site, explore whether the Custom could support your vertical ambitions—even amid constrained urban plots.
3. Historic Sites = Legal Complexity
   Sites with long building histories may carry easements preserved through centuries. Get legal clarity early in the process.
4. Engage Early with Rights of Light Surveyors and Legal Counsel
   They’ll help assess whether the Custom applies and whether it benefits—or limits—your project.

While rarely used in modern development, the Custom of London and the doctrine of Ancient Foundations still carry legal weight. For developers, they can either unlock previously off-limits development potential or present unforeseen barriers.

The key? Knowing where and when they apply—and aligning your strategy accordingly.

Have you ever encountered this Custom in your developments? Curious how it might apply to a site you’re working on? Let’s connect and discuss.