The trend for excavating huge, multi-level basements looks set to spread to London’s suburbs as house prices continue to rise, planning experts have said.Demand for basements is strong in central areas such as Kensington & Chelsea.But Nick de Lotbiniere, head of central London planning at Savills, said: “A rise in house prices has meant it will become feasible for homeowners to look at large basement developments across London and out to the suburbs.“A number of boroughs have begun developing planning policy on the subject.”But Stephen Merritt, who runs development specialist London Basement Company, said it would be a few years before property values outside core Belgravia, Knightsbridge and Mayfair areas were high enough to justify it.

He said house capital values needed to be in excess of £1,800 per square foot for large multi-storey basements to be financially feasible.Councils have begun preparing for a rise in demand, however. Barnet council has added extra planning information on basement developments. A council spokeswoman said: “Permissions for basement extensions in Barnet have risen in recent years.”Tom Bill, residential research expert at property agent Knight Frank, said: “You know the trend has taken hold in an area when a square foot of a basement is worth the same as a square foot above ground. That valuation method has spread beyond prime central areas like Kensington & Chelsea and into Wandsworth, Battersea and Clapham over the last 12 to 18 months.”