News of a possible bid from Mr Walls, a high-profile City figure, came as Servisair rejected Amey's offer as "wholly inadequate".
Mr Walls, a former chairman of the troubled food producer Albert Fisher and of paper group Wiggins, is understood to have received the backing of a venture capital group to mount a bid for Servisair, Europe's largest ground handling company.
News of an interest from Mr Walls, who has been a Servisair non-executive director since 1994, sparked an angry reaction from the Amey chief executive, Brian Staples.
He said that Mr Walls' involvement in the takeover battle was a matter for the Takeover Panel as he had access to confidential information not available to other bidders. Mr Staples added that it would write to Servisair, asking it to clarify Mr Walls' position.
Servisair said that Mr Walls had not participated in any board decisions relating to the Amey bid.