IN the corridors of London's House of Commons, the pocket calculators are out.
Members of all parties are adjusting to the near-certainty of Prime Minister John Major heading a minority administration by the end of the year, and political arithmetic promises to be an essential skill.
Mr. Major's already-troubled government was dealt a massive blow in the fading hours of 1995 when Emma Nicholson, a senior and highly respected Conservative, announced her defection to the opposition Liberal Democrats.
Ms. Nicholson's surprise switch of allegiance came only three months after another respected Conservative crossed the Commons floor and joined the Labour Party. It unleashed a torrent of government abuse on her head.
But amid the cries of "disloyalty" and "betrayal" coming from senior ministers, cooler political heads studied the parliamentary arithmetic of her action. It has left the government with 324 supporters in the Commons and other parties with 321.
The government is up to 30 points behind Labour in opinion polls and, according to most independent analysts, two pending by-elections are virtually certain to be won by opposition parties.
With that, and the possibility of more Conservative defections to come, the prime minister faces the prospect of governing without a parliamentary majority until the next general election, which he must call by May 1997.
Under the British system, that is feasible. In the 1970s, a Labour Party administration ruled for more than a year without an assured Commons majority.
But that may not be an encouraging precedent. After its spell of minority government, Labour suffered a humiliating defeat at the hands of Margaret Thatcher, ushering in 16 unbroken years of Conservative rule.
Political analyst Peter Riddell says the Nicholson defection has given the government "an aura of near-terminal decay and decline." Collapse from within, Mr. Riddell believes, is the biggest threat to its survival.
Similar sentiments are coming from highly placed Conservatives. Sir Edward Heath, a former prime minister and currently "Father" of the House of Commons, on Jan. 1 urged his party to abandon backbiting and close ranks.
Much of the infighting centers on Britain's role in Europe, with several rebel Conservatives pushing Major to reject moves toward closer ties with the European Union.
Nicholson said the "main reason" for her switch of allegiance was that the Major government was "shilly-shallying on the fringe of Europe." She joined the Liberal Democrats because they were a "pro-European party."
But she added that other aspects of the government's conduct had helped to persuade her to switch sides. Last year, after she had voted for disclosure of outside earnings by members of Parliament, a fellow Conservative backbencher had come up to her and given her "a sharp blow in the stomach."
Fuelling the impression that Nicholson's defection had unleashed bitter passions at the highest levels of government, Defense Minister Michael Portillo said she had "a record of disloyalty," and on the government's European policy was "talking awful nonsense."
As the government braced itself for a difficult year, the Labour Party announced Jan. 1 that it intended to force a series of Commons votes to further undermine Major's authority.
A senior Labour official said party leader Tony Blair did not expect to defeat the government on a confidence motion, but would "harass it at every opportunity."