The Yorkshire Post has learned that bosses at the society were alerted to the problem last Thursday, but most staff were only told last night.

In a statement released to its employees the company admitted that among the mislaid information were details printed on staff payslips including bank and salary details.

The mutual – which is the eighth largest in the UK and employs 1,000 staff – has been refurbishing its Albion Street headquarters, in Leeds.

The data went missing when the human resources and marketing department moved to another part of the building, together with the executive management team.

The timing will cause particular embarrassment as the public is sensitive to the handling of personal information after the Government admitted Her Majesty's Revenue and Customs had lost the records of 25m people claiming child benefit.

The Leeds stressed that much of the missing information was already available in the public domain, but urged staff to be vigilant with their accounts and alert the society if they learn of anyone trying to change the address or order a chequebook.

Some were alerted earlier than last night and asked to check their accounts. No problems have been reported. The society said that in the "extremely unlikely event that staff did suffer a loss" it would reimburse them fully.