The consultation document issued by ministers a year ago identified 12 members as the optimum size for each of the eight boards, with four councillors in each region. But deputy prime minister John Prescott this week said: 'The full range of expertise needed can only be achieved at this stage with boards of 13.'
Council representation remains at four on each board.
The Local Government Association said it was regrettable that councillor representation had not been increased as part of the change.
The legislation establishing the agencies allowed ministers to appoint up to 15 members.
The appointments show a heavy Labour bias, despite government insistence that the posts were widely advertised and appointments made in accordance with guidance issued by the Commissioner for Public Appointments. Labour's representation on the boards is twice that of the other parties combined.
The presence of several Unison and GMB officials also means Labour is over-represented among political activists who are not councillors.
The LGA welcomed the strong showing by senior figures of the association. Rita Stringfellow, leader of North Tyneside MBC and chair of the LGA's social affairs and health committee, has been appointed to the north-east board. Ken Bodfish, who heads the UK delegation to Europe's Committee of the Regions and is deputy leader of Brighton and Hove Council, is on the south-east board.
One of the most prominent Tory councillors, Wiltshire CC leader Peter Chalke, also chairs the County Councils Network within the LGA.
Mr Prescott said expertise from education and the trades unions is represented on each board.
But only around a quarter of the members are women, while ethnic minorities make up 5% of the membership.