The Prime Minister called for an alliance of pro-Union parties, together with business and trade unions, to come together to fight to prevent the break up of the UK.

His intervention, in an interview with the Sunday Telegraph, came as the row over Scottish Labour leader Wendy Alexander's call for an immediate referendum on independence continued to reverberate through Westminster and Holyrood.

While Mr Brown defended Ms Alexander as an "excellent leader" of Labour in Scotland, he again distanced himself from her call for a poll on independence, saying he was personally "not persuaded" of the case for a referendum.

"I will do whatever is necessary to ensure the stability and maintenance of the Union," he said.

"I will do anything and everything to ensure that the case for the Union, which has served Britain and the British people so well, is properly heard an advanced.

"I want all unionist parties and all parts of business - employers, managers and trade unions - to work together not only to push the case for the Union but to expose the dangers of separation. Some issues are bigger than party politics and need to be addressed in the common interest."

Ms Alexander threw Labour into turmoil in both Scotland and England with her unexpected call for an immediate referendum, having previously said that a poll on independence was unnecessary.

She has said that the move was intended to expose the "hollowness" of the position of Alex Salmond's Scottish National Party administration which has promised a referendum but not until 2010.

However she has conspicuously failed to win the backing of ministers in Westminster, amid repeated claims that she omitted to consult Mr Brown before issuing her call in a BBC Scotland television interview.