Thousands of apartments which have been bought off-plan could be returned to the London market next year, it has been claimed, with foreign investors disillusioned.

Reasons include the 3% Stamp Duty surcharge that kicks in next April, the fact that overseas investors are now caught by Capital Gains Tax, and the strength of the pound compared with other currencies.

Faisal Durrani, head of research at agent Cluttons, said: “We can expect a flood of supply with non-domiciled investors returning off-plan residential stock to the London market, especially throughout 2016.

“We estimate approximately 60,000 homes are due for completion in 2016 and 2017.

“Of these, we believe between 50% to 60% have been sold off-plan to international buyers. Therefore, it is likely that up to 30,000 properties could be returning to the market in the coming two years.”

NAEA managing director Mark Hayward said: “The significant additional Stamp Duty on potential investment properties bought off-plan will mean purchasers will be unable to escape punitive charges as these homes will miss the April deadline.”

Many off-plan properties were sold, controversially, to overseas investors sight unseen at overseas property fairs.

Market analysts will be looking to see whether the off-plan purchasers will make a profit or take a bath if and when they ‘flip’ their properties so early. The prices they paid, in places such as Nine Elms, were well beyond the means of local first-time and most other buyers.