Mr Porter's death reduced Mr Major's majority to one, and if Labour holds on to Barnsley East, where a by-election is pending, and takes Mr Porter's Wirral South seat, the Conservative Government will be in a minority of one for the first time since Lady Thatcher took office.
Mr Major would be able to struggle on to a general election next May but the symbolism of a minority government hanging on to power with the support of David Trimble's nine Ulster Unionist MPs could harm the Tories. They could spring a surprise and hold the by-election before Christmas but Labour leaders are planning for a campaign in February.
Wirral South, with a perilously thin Tory majority of 8,183, is regarded as winnable by Labour, which is expected to throw everything into the fight for it. John Prescott, the deputy leader, who heads Labour's key- seats strategy, will be in charge of the campaign.
Mr Porter, an MP since 1979, had told friends last month that he had been given six weeks to live after being diagnosed with cancer. He bore his last days with fortitude and good humour, according to friends who visited him in a London hospital.
An outspoken right-winger, Mr Porter, 57, was a tough-talking, sometimes hard-drinking Merseysider, who was educated in Birkenhead. He was well- liked at Westminster, though he was the first backbencher to tell Baroness Thatcher it was about time she "hung up her boots", and he backed Michael Heseltine in the leadership race.
A committed Unionist, he was never afraid to criticise the Government and vigorously challenged the Prime Minister's judgement in accepting the ceasefire by the IRA in an attempt to get Sinn Fein into the peace talks.
His seat, neighbouring David Hunt's Wirral West, is in the comfortable suburbs of Merseyside, where the Tories need to do well to win the general election. Voting in the constituency's five Wirral borough wards in May's council elections put Labour ahead by a whisker. Labour polled 8,517 (37.5 per cent), the Tories 8,340 (36.7 per cent) and the Liberal Democrats 5,539 (24.4 per cent).
Mr Major said of Mr Porter, who was married with five children: "Barry's generous heart and good humour will be much missed at Westminster and in the Wirral. He served both his constituents and country well."
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