British Land and Oxford Properties have agreed a deal to let the 41st floor of the Cheesegrater to insurance company FM Global at almost £85/sq ft — a record for the City of London.

A floor spanning around 7,700 sq ft at the Leadenhall Building is now understood to be under offer to the US-based insurer.

The price eclipses a deal done by Arma Partners in Irvine Sellar’s Shard earlier this year, at what was hailed at the time to be a record at £80/sq ft.

Research carried out by Property Week in August found that average prime rents were £60/sq ft in Q2 in the City of London, compared with £66/sq ft at the end of 2008, before the recession hit.

DTZ and JLL are joint letting agents at the Leadenhall Building. All parties declined to comment.