What happens once the result is known?

Blair back with 150 majority

Despite a bruising campaign, Tony Blair has scored a triumphant third landslide victory, holding on to all but a handful of the seats won from the Conservatives in 1997 and retained in 2001.

He argues that New Labour has become the natural party of government. His hold on Downing Street seems unexpectedly strong and looks certain to serve almost a full term as Prime Minister, with Gordon Brown's ambitions to replace him on hold yet again.

Mr Blair will feel emboldened to promote Blairite standard-bearers, such as Hazel Blears and David Miliband, to the Cabinet. Stephen Byers will be waiting by the phone and Alan Milburn can demand a plum job.

This is a profoundly depressing outcome for the Tories, who have reaped scant reward for an aggressive campaign. Michael Howard vows to stay on to save them from meltdown, but the party plunges into renewed agonies as modernisers warn that it must reinvent itself or die.

The Liberal Democrats have made modest gains, but they lack the critical mass to dictate events given Labour's crushing majority.

Blair wins 80-seat majority

Although Labour has won another clear victory, it has lost at least 40 seats and is only about three points ahead of the Tories in the total vote.

Tony Blair could find himself vulnerable to his left-wing rebels, who have the numbers to make his life uncomfortable, and speculation intensifies over how long he will stay in office. The Prime Minister says he is determined to serve a full term despite rumours that he could bow out after next year's referendum on the European constitution.

Gordon Brown's position is strengthened and he demands the promotion of allies as his price for coming to the rescue of the campaign.

The Tories have made only modest progress, picking up some seats in the South, but losing others to the Liberal Democrats because of tactical voting. They still have fewer than the 209 seats won by Michael Foot during Labour's dog days. Michael Howard stays on for a year.

With nearly 20 gains, the Liberal Democrats have 70 seats and the prospect of considerable influence at Westminster.

Blair's majority cut to 40 seats

Labour has lost 60 seats, from Sussex to the Scottish Highlands, and is only a percentage point ahead of the Tories in the popular vote, winning the backing of just over one in three voters.

Although some of Tony Blair's predecessors would have loved a similar working majority, his future looks precarious. He reshuffles his Cabinet team, Gordon Brown secures the promotion of several key lieutenants and Mr Blair appears to prepare for an orderly handover of power.

Left wingers, who now have the power to overturn the Labour majority, will not wait, however, and immediately begin moves to depose Mr Blair.

The Conservatives still have not made dramatic progress, although they now have 210 seats and seem to be recovering after a decade in the doldrums.

The Liberal Democrats also scent influence, with the outcome of all parliamentary votes depending on their stance. They picked up another 15 seats.

Labour has to scrap its plans for a national identity card scheme given the strength of opposition in the new-look Commons. It braces itself for a fresh battle over anti-terror laws.

Blair routed in hung parliament

A disastrous performance by Labour, losing 110 seats as they are wiped out in the south of England and fall behind the Tories in the popular vote.

Mr Blair looks doomed, facing recriminations over the Iraq war following a catastrophic loss of trust in him among the voters.

A stunned Prime Minister knows his leadership is doomed and decides to step down as soon as a contest can be arranged. In the meantime, in conjunction with Gordon Brown, he begins working on a makeshift cabinet.

The Liberal Democrats, basking in the glory of a contingent of 85 MPs, find they are offered cabinet places and a review of the electoral system.

The Conservatives, who have made more than 80 gains, are back in business, having renewed their appeal to Middle England. A buoyant Michael Howard's leadership is secured.

Labour is forced to woo the Liberal Democrats on contentious legislation, including plans to reform the council tax and overhaul the pensions system. The Liberal Democrats demand the withdrawal of British troops from Iraq by the end of the year.

Tories win as Blair humiliated

The most stunning result in electoral history hands Downing Street to Michael Howard. With more than 330 seats, the Tories have broken through in every part of England and even gained seats in Scotland and Wales.

Mr Howard hands key cabinet posts to David Davis, Liam Fox, Oliver Letwin and young guns George Osborne and David Cameron. He begins work on his "timetable for action".

Labour goes into meltdown, having lost more than 180 constituencies in its worst election performance since 1983.

A humiliated Tony Blair resigns immediately and senior party figures turn to Gordon Brown to lead them out of disaster. Left-wingers look for a challenger to stop him having a clear run.

The Liberal Democrats have a respectable haul of 60 seats and because of the tiny Tory majority are serious players at Westminster.

Mr Howard embarks on a radical reshaping of public services, with school vouchers offered for private education and subsidies for hospital patients who go private. Tory ministers enter fraught negotiations with their opposite numbers in Brussels.