Former Leighton boss Wal King repaid $40,000 worth of unauthorised expenses – including trips to Madrid, a $780 meal at Sydney's Rockpool restaurant and stays at luxury hotels – that he billed to a company credit card in the weeks after he had left the construction giant.

A Fairfax Media investigation can also reveal a small number of senior Leighton staff were so concerned by a $6 million consultancy awarded to Mr King upon his 2011 departure that external legal advice was sought to determine if it might have breached Australian corporate laws that apply to retirement benefits.

Wal King's exit entitled him to $6 million in consultancy fees over three years, a company credit card, an office and IT support. Credit:Rob Homer

The legal advice was sought in July 2011 after it was discovered that the terms of the consultancy agreement organised before Mr King's departure meant he would be able to invoice Leighton for $6 million in fees over three years without having to provide any services.