British Land has said it will replace “mega-bolts” on 11 floors of its Cheesegrater skyscraper in the City as a “precautionary measure” following a probe into why two bolts fell from the 47-storey tower in November.

Parts of two of the 3,000 5-inch diameter bolts used in the City’s tallest building broke away from the structure, causing the developer to fence the building off.

It also admitted today a third had also broken off.

All the bolts have been checked and the investigation found the failures caused by so-called “hydrogen embrittlement” - growing cracks in the metal caused by the presence of hydrogen in the manufacturing process.

As a precautionary measure British Land’s contractors are replacing bolts in a similar position to those that broke, affecting 11 tenanted floors and meaning potentially dozens of bolts could be replaced.

British Land said engineers Arup had confirmed there was “no adverse effect on the structural integrity” of the building.

But the problems are an embarrassment for the tower which has attracted tenants far less quickly than its rival in London’s insurance district, the Walkie-Talkie.

The company confirmed that the Cheesegrater’s own designer, Lord Rogers, is moving his architectural practice into the skyscraper, as revealed by the Standard in October.