By Laura McGuire Engineering firm Costain is moving its headquarters from Maidenhead to the City of London, to a building with a tasty nickname. Today the firm said it would be relocating to 70 St Mary Axe, a London tower also known as the Can of Ham. Costain will occupy all 17,181 sq ft of the 7 floor of 70 St Mary Axe as it increases its presence in the capital. The move is expected to be completed in the second half of 2024. The office will have capacity for approximately 125 desks, increasing Costain’s existing London capacity by around 400 per cent. As part of the move, Costain will vacat…