The Government is facing a legal challenge that could force it to change its decision to hold the Budget on 9 April.
The Conservative Party, the Scottish National Party and Plaid Cymru are taking legal advice because the Budget would be presented during the campaign for the Scottish Parliament and Welsh Assembly elections on 1 May.
Downing Street and the Treasury said the date would not breach Whitehall rules laying down a period of "purdah" during election campaigns.
The opposition parties say issuing a principal statement of government policy could be a breach. The SNP and Plaid Cymru held talks at Westminster last night. A Tory spokesman said: "We are looking at the legality of it." The Electoral Commission, which supervises conduct of elections, may be asked to intervene.
Alex Salmond, the SNP's leader at Westminster, said Labour's decision was "totally unacceptable" and an "abuse of Scottish democracy". He cited the precedent of a judicial review in 1996 which forced John Major, Prime Minister at the time, to scrap a television interview during the local election campaign in Scotland.
Gordon Brown announced yesterday that his Budget would take place after the end of the tax year for the second consecutive year. Last year it was put back after the death of Mr Brown's baby, Jennifer. This year the reason is thought to be the likelihood of war in Iraq.
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