Scotland Office deputy David Cairns has become the first minister to quit the government, The Herald understands.

Michael Settle: "A feverish day in Westminster"

Pressure was mounting on Gordon Brown today as a minister quit the government in protest over leadership.

As Labour's ruling executive rejected rebel demands for leadership nomination papers to be sent out, David Cairns left his job at the Scotland Office.

At least one ministerial aide has also indicated they are ready to resign, telling the Press Association Mr Brown was in his "death throes", and they were waiting "until the time is right".

Mr Cairns is a close ally of one of the rebel ringleaders, former Government Whip Siobhain McDonagh, having worked as her assistant before entering Parliament as MP for Inverclyde. He was not answering calls today or yesterday. A Downing Street spokesman refused to comment.

More than 10 Labour MPs have asked for leadership nomination papers to be sent out to all their colleagues ahead of the party's conference in Manchester this weekend, a move which they believe would increase the chances of unseating Mr Brown.

However, a meeting of the National Executive Committee today dismissed those calls.

A party spokesman said the NEC had agreed "without dissension" that the forms did not need to be issued.

The chaos within Labour continued despite a warning from former Foreign Secretary Margaret Beckett that the public "would not forgive" the party for infighting amid the economic crisis.

She told BBC Radio 4's Today programme that "no-one could be happy" with the current situation, but this was not the time for a "substantial debate" about the leadership.

"When we are in Government and we have a Prime Minister and there are very serious international concerns about the economy and so on, I really don't think that most people will think we should be wanting to spend our time on discussing whether we should have a different Prime Minister," Ms Beckett said.

Chancellor Alistair Darling also rallied round the Prime Minister, insisting he was the "right person" to lead the country through turbulent times.

"I have every confidence in Gordon Brown," he said. "I believe he is the right person to lead this country and to lead our party and I know that at the conference next week he will set out his vision for the future."

The NEC had been considering a technical point over whether party rules meant nomination forms should always be sent out before conference, rather than just being available on request.

Some 71 MPs have to nominate a candidate in order to spark a leadership challenge, and the rebels argued that many were being put off by having to come forward and ask for a form.

However, a statement from NEC chair Dianne Hayter said: "The Labour Party national executive committee is in agreement that internal procedural debates will not divert the Labour Party from our mission of building a fairer Britain and helping people through these challenging times."

She added: "The Labour Party has followed this procedure for 11 years, as long as we have been in government under these present rules, and it has not required the issue of nomination forms at any time."