Opposition parties yesterday demanded the Scottish Executive accept the advice of its own expert group and alter plans for proportional representation voting in local council elections to make them fairer.

First Minister Jack McConnell agreed to replace first-past-the-post (FPTP) with the single transferable vote (STV) in the post-election coalition deal with the Lib Dems, despite strong opposition from Labour backbenchers and councillors who favour the status quo.

But an interim report by the independent STV working group recommends ministers go further and alter the Local Governance (Scotland) Bill, now in parliament, to allow some wards to have five seats and others, in the remotest areas, to have two.

This flexibility would allow wards to be allocated more accurately in terms of natural communities, geography and parity, the experts said.

However, aides to McConnell said it would take "a great deal of persuading" to change the plans already agreed with the Lib-Dems.

Socialist leader Tommy Sheridan, who is on the Local Government Committee that will quiz Lib-Dem and Labour ministers on the bill next week, said that the report was a "huge embarrassment" to the coalition.

The report, issued on Wednesday, cites evidence that the coalition’s plans would be the least proportional system of PR that exists and that allowing five-member wards would improve proportionality.