The NatWest is in negotiations with a number of US law firms interested in taking several floors of its newly-renamed International Financial Centre, the tallest building in the City.

Ashurst Morris Crisp has been advising NatWest on leasing the tower, which was closed three years ago following damage caused by an IRA bomb.

A NatWest spokesman said the company expected to be able to announce a number of lettings in a few weeks.

The company is targeting foreign, particularly US, firms which are starting offices in the City and may need to expand later and so would need flexible leases. Space is available on some floors at £45 per sq ft.

Simon Cookson, Ashursts property partner who led the team advising NatWest, said his team had developed four kinds of lease for the building: serviced offices with all facilities available at a premium rent; a short-term flat-fee lease which included a service charge in the rent; a long-term traditional lease; and a shorter term conventional contract.

“The idea is that by having these different forms of lease ready to be signed, we cut out lengthy negotiations with prospective tenants,” he said.

Cookson has also just advised NatWest on the £41m sale of its adjacent low-rise buildings, in a triangle bounded by Threadneedle Street and Old Broad Street, to the Singaporean JPI Group, which was advised by Eversheds.

JPI is planning to convert the properties into a five-star hotel, offices and shops. Cookson said: “With the market rumour that Labour was about to increase stamp duty to 7 per cent, we had to complete before the budget. In the end stamp duty did go up from one per cent to two so we saved the companies an extra £41,000.”

He added: “The most difficult thing was ensuring that some protection from over-development was written into the documents.

“NatWest is retaining a patch of open green land next to the site which it uses for functions at Gibson Hall. It did not want JPI to build a huge tower that would spoil this open space… You cannot rely on the planning rules to protect you.”