British Land and Blackstone Group have signed leases with Swiss bank UBS to develop a new 700,000 sq ft building on the site of 4 and 6 Broadgate, in the City of London. The new building represents a significant commitment by UBS to the City and Broadgate in particular, British Land said. UBS is currently the largest tenant in Broadgate and negotiations over its renewing its presence on the site had been ongoing for months.Development costs will be around £340m (excluding land and interest costs) with the practical completion to shell and core scheduled for the second half of 2014. The deal is estimated to have a total value of about £600m. It will be seen as an especially good deal for Blackstone, which acquired half of the Broadgate estate last summer after property prices had slumped following the credit crunch.The initial headline rent is £54.50 per sq ft with annual RPI linked increases with a weighted average lease length of 18.2 years. Reports today said the new UBS building will not be a tower due to height restrictions.