Selling point for flats worth £250m

Dolphin Square was built by Costain between 1935 and 1937 on a 7.5 acre riverside site and cost £1.5 million. At the time, the 1,250-flat block was the largest in Europe.

In 1963, Westminster council bought a 70-year lease on it for £4.5 million (equivalent to £50 million today) giving it full control of running the square.

Westminster set up the Dolphin Square Trust, comprising councillors and council officers, gaveit a loan to buy a 70-year sublease, and the right to decide who lived there and how much rent they paid.

There are two kinds of tenants. Many who have lived in the square from before 1990 pay controlled "fair rents" of between £60 and £180 per week. Tenants who moved in more recently pay higher "market rents" of £300 to £1,200 a week.

The freehold is currently owned by Friends Provident, which may want to sell the flats as they become vacant - many will be worth £500,000 or more on the open market.

The value of Dolphin Square as a whole with vacant possession has been estimated at £250 million.

To take control of the flats Friends Provident must buy out the leases. It has reportedly offered £70 million to the trust which would include windfalls of some £13,000 each for those prepared to move.