Questions are being asked over the suitability of the base of the tower crane that collapsed onto a block of flats in Liverpool last Monday

The accident happened on Bowmer & Kirkland’s £28m mixed-use Kings Dock Mill site. Residents were left trapped inside their flats and the crane driver, who suffered injuries to his head, chest and legs, remains in hospital.

Terry Duxbury, co-director of the United Crane Operators Association, said several of his members had told him that the base was not appropriate for the crane. Two other sources said they understood the problem was with the base.

A spokesperson for HTC Plant, which leased the crane, said: “We will investigate until we reach a conclusion in this matter.”

Bowmer & Kirkland said the firm was unable to comment as the Health and Safety Executive investigation was continuing.