Labour's chances of winning the Glenrothes by-election were dealt a fresh blow yesterday after the leader of Scotland’s Catholics condemned the party’s record on moral issues.

In a letter to be read in parishes in the constituency today, Cardinal Keith O’Brien urges all Catholics to consider Labour’s position on abortion, the ban on Catholics succeeding to the throne and nuclear weapons before casting their vote.

His appeal to the constituency’s 6,000 Catholic church members caused deep anger within the Labour party, which believes the church’s role in the Glasgow East by-election in July helped to cost it the seat.

On the eve of the Glasgow vote Bishop Joseph Devine, whose diocese covers the constituency, accused Labour of “violating moral law” and said it had lost the electorate’s trust. Labour lost the seat to the SNP by 365 votes.

While the Glenrothes constituency has fewer Catholics than the East End of Glasgow, O’Brien’s attack could prove decisive on November 6. The SNP is seeking to overturn Labour’s 10,500 majority and is tipped to win the seat, following the death of the sitting Labour MP John MacDougall.

In his message to parishioners, O’Brien said Catholics had a duty to vote and to ensure that candidates are made “well aware that an active community of Catholic citizens exists here in this constituency”.

He added: “There are obvious matters which should concern every Catholic . . . the continued commitment to the renewal of the £24 billion Trident nuclear weapons system; the depressing reality that, over 40 years after its passing, the Abortion Act has not been repealed or amended in such a way that it will save life rather than continue to destroy life; the continued existence of the overtly sectarian Act of Settlement.”

O’Brien also criticised the government’s human fertilisation and embryology bill which will pave the way for research using hybrid human and animal embryos.

Some Labour strategists fear the intervention could prove significant. One said: “This isn’t Glasgow East, which had a huge swathe of Catholic voters,but his comments count because it doesn’t take much to swing the result if the majority is going to be tight.”

Another accused the Catholic church of pursuing an anti-Labour agenda. “This is another fillip from the cardinal to the SNP. I’m surprised that he doesn’t think that homelessness and pensioner poverty, where nobody would dispute our commitment, are things the church should be considering as well as Trident,” he said.

John Park, the Labour Mid-Scotland Fife MSP, said: “I think you need to separate politics from religion. I’m sure voters will consider what all the candidates are saying and the wider picture before they go to vote.”

Labour campaign insiders said Gordon Brown’s handling of the economic crisis, including his bailout for British banks, has boosted the morale of local Labour campaigners but they admitted they were still suffering from an acute shortage of volunteers.

Labour has resorted to offering free buses and lunch to any party members prepared to give up a day to campaign in the constituency.

Yesterday the nationalist-run Fife council pledged to freeze council tax until 2011, the final year of the SNP government’s current parliamentary term, to boost its by-election chances. The SNP government said it would make available resources to enable councils across Scotland to do the same without cutting services.

Peter Grant, the SNP candidate, said: “The SNP knows the impact rising prices have on household budgets and we are determined to do everything we can to lift that burden.”

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