The director of the Twentieth Century Society criticised culture secretary Jeremy Hunt after it emerged he was secretly lobbied by an interested party days before deciding not to list Broadgate.

Catherine Croft said the letter from the chief executive of Swiss bank UBS warning it could leave London if Broadgate were listed raised the question whether Hunt had “acted properly”.

The letter was sent by Carsten Kengeter a week before Hunt made his controversial decision to overrule English Heritage’s advice to list at grade II*.

He warned that a decision to list would force UBS to “fundamentally reconsider our occupation strategy”. Hunt denied he had been swayed by commercial pressures.