The number of London house sales breaking the £1m price barrier is expected to rise by 47% by 2018, Savills has said.

However, yesterday another London agent said sales are getting stickier.

Ed Mead, of Douglas & Gordon, said that time on the market has doubled from this time a year ago to 4.5 weeks, and that it is taking much longer to get from acceptance of offer to exchange – at around 11 weeks.

If Savills is correct, new growth would represent a further expansion of a market that has already grown by 165% in the past five years.

In 2003, just 1,825 £1m-plus sales were recorded by the Land Registry, a figure that rose to 7,529 last year.

By 2018, the annual total is expected to exceed 11,000 in response to forecast price rises, Savills says.

The growth in the number of high-value sales will also be driven by once unfashionable parts of London becoming “primed”.

Ten years ago, just over half of sales worth £1m or more were concentrated in two central boroughs – Kensington & Chelsea, and Westminster – with 569 and 370 sales respectively.

Last year, while these two central boroughs still accounted for a third of this high-value market place, four other boroughs – Wandsworth, Hammersmith & Fulham, Camden and Richmond upon Thames – each had more than 500 £1m-plus sales recorded by the Land Registry.

Only two of London’s 33 boroughs – Barking & Dagenham, and Newham – did not see any £1m-plus sales recorded by the Land Registry in 2013.

Lucian Cook, head of residential research at Savills, said: “In the past five years, we have seen £1m sales increasingly extend into areas such as Acton, Dalston, Herne Hill, Tooting Bec and Blackheath.

“In the next five years such sales are expected to become significantly more concentrated in emerging locations such as Streatham, Kingston, Borough and Northwood.”

Savills is also forecasting Brixton as a future hotspot where £1m price tags will be seen. Other tips are Earlsfield, Wanstead and Crystal Palace.