Brown's new poll test as Miliband weighs in

The Prime Minister paid generous tribute to Glenrothes MP John Mac-Dougall, who died of cancer in the early hours of today.

The death of Mr MacDougall, 60, triggers a by-election in Mr Brown's backyard - and the prospect of another defeat by the Scottish National Party.

The poll looks set to be held in October, raising the prospect that it could ruin the Prime Minister's much-anticipated "relaunch" at the Labour conference in Manchester next month.

The Glenrothes seat neighbours Mr Brown's Kirkcaldy and Cowdenbeath constituency and the SNP will be confident of overturning a 10,000 majority from the 2005 election. Less than three weeks ago Labour lost Glasgow East's 13,500 majority to the nationalists, who last year won the Scottish Parliament seat that covers Glenrothes.

Former oil rig construction yard worker Mr MacDougall was diagnosed with the asbestos-related mesothelioma more than two years ago.

Mr Miliband sparked speculation about a leadership bid last month after he wrote an article calling for a new approach for Labour. When asked this morning if he had any regrets, he told BBC Radio 4's Today programme: "No. I think the article set out a very clear agenda for defending the record of the Government, for advancing a clear vision of the future, of Britain's new place economically, socially and internationally."

The Foreign Secretary, speaking from an emergency EU foreign ministers meeting in Brussels, said: "I am fully focused on dealing with the situation in Georgia. I am working very closely with Gordon on that - end of story."

But in a remark that may be seized on, Mr Miliband said that being Foreign Secretary was "my job at the moment".

Mr Brown today revealed he had visited Mr MacDougall on Monday. In a statement, he said: "Over three decades he has been a good personal friend. Our heartfelt condolences go to his widow, Cathy, to his son and daughter, Scott and Julie and to his mother and sister."

In a further sign of government disarray, employment minister James Plaskitt today ducked questions about Mr Brown. When asked by Radio 4's World At One if rising unemployment would further destabilise the Prime Minister, Mr Plaskitt replied: "I'm not commenting on that issue." After an on-air intervention from his press officer, Mr Plaskitt then said: "The answer's 'No'."