Mr Stephen became Scotland's deputy first minister in 2005

Nicol Stephen said the Lib Dems would not support other Labour ministerial nominations after the May election.

The deputy first minister's warning came after Mr McConnell said Labour may drop the Lib Dems as coalition partners and form a minority administration.

Mr Stephen said Labour may have to look to the Tories to vote them into office.

"If Labour is in a minority situation and trying to form a minority administration, let's be absolutely clear on this - the Liberal Democrats would not vote for Jack McConnell as first minister," he said.

'Very interesting'

After warning that his party would also not support other Labour ministerial nominations, he said: "In those circumstances, the Labour Party would have to look to the Conservatives to vote the party into office.

"It would be a very interesting question to see whether we would have a Labour minority government effectively supported by the Conservative Party in Scotland."

Mr Stephen said the Conservatives had previously indicated they might be willing to support Labour in those circumstances.

"It will be very interesting to see if that's what Jack McConnell and Annabel Goldie are now intending," he added.

Decisions about who runs Scotland are for after the votes are in and counted Conservative spokesman

Mr McConnell's two preferred options were said to be the continuation of a two-party coalition with a majority of seats, or a minority government in which Labour would seek support for every vote.

His least-preferred option was said to be a three-handed coalition involving the Lib Dems and the Greens.

However, the Conservatives accused the Lib Dems of going in a huff "at the first sign that they might be no longer relevant".

A spokesman said: "If Nicol Stephen has fallen out with his great buddy of the last seven years, then he should do the decent thing and call off the coalition now - that would be the honest thing to do.