Property company British Land has secured a total of 465,000 sq ft of new lettings at its recently completed London office developments since February, with an additional 154,000 sq ft under offer. Tim Roberts, Executive Director and Head of Offices, said that the level of letting activity in the London office market has increased significantly in the first quarter. "We've seen rental values firming with all of our recent deals accretive to value. Our office portfolio is now 92% let with an average lease length of nine years to first break." "We continue to see good levels of interest in our remaining space and are optimistic about the outlook given the shortage of high quality prime Grade A space over the next few years."Together the new lettings increase the group's overall office occupancy rate from 84% to 92% and have a weighted average lease length of 15 years to first break.The terms agreed exceed the December 2009 estimated rental values and add an additional £19m of headline rent per annum to the group.At Regent's Place in the West End the whole of 10 Triton Street (117,000 sq ft) has been let to Aegis and at 20 Triton Street, 89,000 sq ft has been let to Gazprom Marketing & Trading and a further 30,000 sq ft is under offer. In total, 57% of these two new buildings have now been let.