It is to put down a Commons motion of no-confidence in the Cabinet's weakest and most vulnerable member, Douglas Hogg, the Minister of Agriculture, for debate next Monday.
The last time a vote of censure against an individual minister brought a Government down was just over a century ago, in June 1895.
But Labour deliberately pulled short of an all-out vote of no confidence in Her Majesty's Government, the constitutional device to bring a government down and force a snap election - if carried.
There was no certainty last night that the Ulster Unionists would side with Labour even though there has been considerable unhappiness in Northern Ireland over the "mad cow" crisis.
Nevertheless, Labour's attack will add to the atmosphere of uncertainty at Westminster and the perception of instability in the Government, There will be much behind-the-scenes horse-trading before Monday's 10pm vote, which is technically on a motion to reduce Mr Hogg's salary.
Martin Smyth, the Ulster Unionist MP for Belfast South, said that his party would consider voting with the Labour Party.
"We will, if necessary, vote against the Government as we would be prepared to vote against the Labour Party if we felt theirs wasn't a proper motion," he said.
But the last time the House of Commons voted on BSE, in November, the Government won by only one vote and the Ulster Unionists voted with the Opposition.
Paul Tyler, the Liberal Democrats' spokesman, said his party would support Labour's motion, although he was critical of its tactics.
"When the Liberal Democrats moved an identical motion at the height of the BSE crisis just after the retreat at Florence, Labour failed to support our farmers," he said.
But John Prescott, Labour's deputy leader, said last night: "How can a man responsible for one of the biggest bills for incompetence this country has ever seen be worth a ministerial salary?
"We will hold Douglas Hogg to account for the pounds 3bn his government has cost Britain."
A Conservative spokesman said last night that the party was confident of winning.
"The Government is taking forward policies to deal with this complicated issue in a responsible manner. In stark contrast, Labour are indulging in parliamentary gimmicks and personality politics," he said.
Labour's Chief Whip, Donald Dewar, told Channel 4 News: "We think that, on the merits of the matter, the other parties ought to be in our lobby."
Mr Dewar hinted that Labour would call a vote of confidence in the Government if it won. "If the Government get into that kind of difficulty then they themselves are deeply wounded and at risk," he said.
Some Labour MPs said last night that Mr Dewar had modified his position, having previously argued that a no-confidence motion which would simply unite the Tories, and even push the Unionists more firmly into the Tory embrace.
Monday votes are traditionally precarious for the Opposition, because MPs take their time getting back to Westminster after the weekend away.
As the Commons is at present tied, with 322 Conservatives votes to 322 for the combined parties of the Opposition, Mr Hogg will in all probability survive his ordeal by fire next week.
The Opposition is not expected to be able to muster an outright Commons majority until after Labour's expected win in the Wirral South by-election at the end of the month.
But even then, there will be doubt over Labour's ability to deliver the killer blow. David Trimble and his nine-strong group of Ulster Unionists are genuinely torn between the Tony Blair devil and the deep blue sea of John Major.
The Unionists are as ever open to offers, but neither party leader appears willing to make grubby public bids for their support.
Although the Government was able to take comfort from another fall in unemployment yesterday, it faced a further Bank of England challenge on interest rates, and the Wirral South by-election campaign was dominated by a warning from the multinational company Unilever, which employs many people in the constituency, that any future investment could be jeopardised by an opt-out from European monetary union.
The spectre of increased lawlessness in deprived, inner city ghettos will be raised today by Gordon Brown, the Shadow Chancellor.
Adding to pre-election tension, Mr Brown will warn today that: "The re-election of the Tories would risk the creation of a fifth-term underclass that would take us down the road of America, with no-work and no-go inner-city areas plagued by lawlessness."Reuse content