The scrutiny committee will hold the independent mayor to account. But ever since scrutiny was introduced there have been fears it would be used to settle political scores.
Mr Walker (Lab) is chair of Cleveland police authority which pursued criminal and disciplinary proceedings against the former detective superintendent for four years.
He is viewed as backing Cleveland chief constable Barry Shaw, who earlier this year accused Mr Mallon of being 'at the centre of an empire of evil' (LGC, 14 February).
A Middlesbrough source said: 'All is not well within Middlesbrough. There is a personality clash between Ken Walker and Ray Mallon.
'As chair of the police authority Ken Walker made a point of supporting the chief constable. He made a great mistake by not stepping back.'
Mr Mallon's cabinet includes Labour deputy mayor Bob Brady (Lab), executive member for law and order Barry Coppinger (Lab), two further Labour members including new group leader Paul Thompson, one Conservative and one independent.
Mr Mallon, viewed by the public as the police officer who brought zero tolerance to Middlesbrough, pleaded guilty to misconduct during his time with the force. But he insists he only did this in order to run for mayor.
-- Mayors in North Tyneside MBC, Lewisham LBC, Newham LBC, Watford BC, Doncaster MBC and Hartlepool BC have appointed their cabinets. In Watford two opposition members have yet to confirm they will accept their positions.