Basement Conversion Drawings in City of London

Where in City of London does a basement conversion actually get determined?

Every City of London postcode district we draw in, the stock that dominates it and the authority that validates a basement conversion there. City of London fees below are the statutory England rates for 2026, not basement conversion estimates.

What changes about a basement conversion in each part of City of London?

Roof pitch, wall build-up and plot depth change every few City of London streets, and each one changes what a basement conversion can achieve at that address.

• Barbican (EC2Y) — Brutalist listed estate defines Barbican, where listed brutalist apartments (barbican estate) set what a basement conversion can do. Post-war slab foundations make basements here expensive and rarely viable across EC2Y. Any Barbican basement conversion is validated by City of London Corporation, with Barbican Centre the usual Barbican reference point on the site plan.
• Smithfield (EC1A) — a basement conversion in Smithfield starts from mostly commercial, residential lofts, and Smithfield reads as Georgian and Victorian commercial. Victorian cellars here convert without planning permission when the footprint and external appearance are unchanged in EC1A. City of London Corporation assesses Smithfield basement conversions against its own Smithfield character guidance, and the location plan we draw for Smithfield references Smithfield Market.
• Fleet Street (EC4) — basement conversion work in Fleet Street means mostly commercial, residential conversions. Fleet Street is Georgian and Victorian commercial. Victorian cellars here convert without planning permission when the footprint and external appearance are unchanged throughout EC4. City of London Corporation decides the Fleet Street application, and Royal Courts of Justice anchors the Fleet Street location plan.
• St Paul's (EC4M) — Listed heritage commercial core defines St Paul's, where mostly commercial, listed residential set what a basement conversion can do. Victorian cellars here convert without planning permission when the footprint and external appearance are unchanged across EC4M. Any St Paul's basement conversion is validated by City of London Corporation, with St Paul's Cathedral the usual St Paul's reference point on the site plan.

What local planning policy applies to a basement conversion in City of London?

City of London conservation designations: there are 27 across City of London Corporation, Whitefriars, St Paul's, Barbican among them. Designation costs a City of London owner the permitted-development route: a basement conversion then needs a £548 householder application over 8 weeks, in place of the £249 prior approval route that takes 6 weeks. Barbican is the City of London designation that most often changes a basement conversion design.

City of London and Article 4: Multiple Article 4 Directions around office-to-residential, demolition, and shopfront changes. A basement conversion planned at a EC1A address is checked against that direction first; City of London Corporation publishes the City of London extent, and the EC1A line rarely follows the City of London boundary you would expect.

What City of London is built from: Very limited residential — Barbican Estate (listed post-war), Golden Lane Estate, modern luxury flats; overwhelmingly commercial. Overwhelmingly commercial; residential planning extremely constrained; one of the two highest listed-building densities in London. That mix decides the basement conversion route in City of London more than the postcode does, and it is what a City of London Corporation case officer reads first. A householder application costs £548 paid to City of London Corporation direct, with 8 weeks to a decision once validated.

Who decides a basement conversion on the edge of City of London?

• Tower Hamlets — cross the City of London boundary and Tower Hamlets Council takes the basement conversion instead, applying 58 conservation areas of its own around E1. We re-price basement conversions at the City of London edge because Tower Hamlets policy and City of London policy rarely align on basement conversion depth.
• Southwark — adjoining City of London, with 43 conservation areas centred on SE1. A basement conversion on the far side of the City of London line is determined by Southwark Council, so the City of London quote for basement conversions is checked against Southwark guidance before it is issued.
• Westminster — the Westminster boundary runs against City of London, so a basement conversion a street from City of London is decided by Westminster City Council instead. Westminster runs 56 conservation areas across SW1 and its neighbours, which is why basement conversions priced for City of London are re-checked against Westminster policy whenever the City of London address sits on that edge.
• Camden — the Camden boundary runs against City of London, so a basement conversion a street from City of London is decided by Camden Council instead. Camden runs 40 conservation areas across NW1 and its neighbours, which is why basement conversions priced for City of London are re-checked against Camden policy whenever the City of London address sits on that edge.

Sources for this City of London basement conversion page: borough policies maps and conservation-area registers (2025–26), Royal Mail postcode district boundaries, the Town and Country Planning (Fees for Applications) (England) Regulations, the Town and Country Planning (General Permitted Development) (England) Order 2015 as amended, and the Party Wall etc. Act 1996.