Development of one of the largest office schemes in the City of London remains in the balance as the much delayed completion of a deal to sell the site is to be extended further into a second year.

Spain's Metrovacesa has a deadline today to pay £240m for the 1m sq ft development site around Bucklersbury House next to Bank Underground station, which it agreed to buy from Legal & General, the insurance group, in the summer of 2007.

The Spanish company is in the midst of a broader overhaul of its corporate structure as well as refinancing parts of its €7bn (£5.5bn) of debt, and has asked L&G for a further extension.

The two parties were last night in final negotiations. There is broad agreement between the two sides that the payment will need to be rolled over again, although the terms of the deal are still being finalised.

Metrovacesa wants an extension of up to 12 months, although L&G is thought to be reluctant to go beyond three months.

Financial Times