HSBC is in talks to buy back its UK headquarters in Canary Wharf for up to £300m less than the price it sold the tower to Spanish property company Metrovacesa only a year ago.

Metrovacesa has until the end of November to refinance a £810m loan with HSBC on the tower, which became Britain's most expensive building when it was acquired in a £1.1bn sale-and-leaseback deal at the peak of the property boom last summer.

Metrovacesa, which has been forced to sell Spanish assets at a loss as it looks to restructure more than £7bn of debt, has failed to raise money from other investors. Those close to the negotiations say a sale to HSBC is now the most likely outcome.

Metrovacesa valued the building at about £1bn in the summer although agents say that has now fallen to about £800m. It confirmed a sale to HSBC was an option but insisted there were others, including refinancing. HSBC has offered a new debt package but Metrovacesa would need to find about £200m in additional equity.

The Spanish company could also be forced to walk away from a commitment to buy one of the City of London's largest development sites. Metrovacesa agreed to buy the Walbrook Square scheme from Legal & General for £240m last summer and it has until the end of this month to pay the money. Should it forfeit, the company would lose a deposit of about £10m although the move would be opposed by Legal & General.

In Spain, Metrovacesa is in talks with various creditors about refinancing parts of its €7bn debt and is understood to have sought a waiver on the terms of a syndicated loan worth €3.2bn. The covenant on this called for fresh capital raising before the end of this year.

The company has also been under regulatory pressure in Spain to increase its free float from the current 9.7 per cent to 25 per cent.

It said in a recent filing that "adverse market conditions" had forced it to abandon attempts to increase its market-traded equity.

Lazard and Goldman Sachs are advising Metrovacesa and shareholders about restructuring the debt.