REPLACING huge bolts on a London skyscraper has cost structural steel firm Severfield £1m.

The North Yorkshire company used a trading update this week to reveal the costs it has incurred for work to examine and replace bolts on the Cheesegrater building in the City of London after two bolts each the size of a human arm broke in the 737ft tall skyscraper in November.

It is understood that one fell from the 15th floor to the ground, while another fell from a lower level but stayed within the distinctive sloped building’s framework.

British Land, the building’s co-developer, said at the time an investigation with contractor Laing O’Rourke and structural engineers Arup had begun.

The loss of the bolts - which connect the building’s “nodes” to its “megaframe” – did not affect its structural integrity.

The Cheesegrater building - designed by architect Richard Rogers - got its wedge shape which earned it the Cheesegrater nickname to help preserve sightlines of St Paul’s Cathedral.

The building’s principle tenant is insurance group Aon and in October last year the property broke City records when American insurance group FM Global agreed a deal to lease its 41st floor for £85 a square foot.

Severfield – the UK’s biggest structural steel company – provided 18,000 tonnes of steel for the Cheesegrater and said in the update that it was in talks to work out where liability for the bolt replacement programme lies. It added the programme to examine and replace the bolts - which range from 20cm to 120cm long and have diameters of between 5cm and 7.5cm - is likely to last until the end of the year.

It added that the costs are seen as exceptional and should not affect underlying profitability for the current year.

Severfield, based in Dalton, near Thirsk, said that while its UK order booked had strengthened recently, demand at its Indian business India had softened. The combined order book stood at £230m.

Severfield has worked on a series of landmark building, including The Shard skyscraper, London 2012 Olympic venues, the Emirates Stadium for Arsenal Football Club, Wimbledon's Centre Court roof as well as Heathrow's Terminal Five and Terminal Two developments.