The most expensive — and arguably the nastiest — mid-term election in US history shuddered through its final hours yesterday after an avalanche of last-minute spending and amid a blizzard of “dirty tricks” claims against both sides.

With Republican control of Congress and the prospect of hobbling President Bush’s last two years in the White House at stake, there was anecdotal evidence from key states such as Virginia and Ohio that turnout could be the highest in decades for a Congressional election.

Mr Bush voted at sunrise in Texas, where he issued a plea to Americans to exercise their democratic rights. But even as he spoke, problems with electronic voting machines, allegations of ballot-rigging and claims of intimidation began. The protests were loudest in the most closely contested states, mostly from Democrats, many of whom are convinced the last two presidential elections were stolen from them.

The FBI said that it was investigating complaints that voters in Virginia had received telephone calls with misleading information about where their nearest polling station was located. The bogus calls included some from people claiming to work for Jim Webb, the Democratic senatorial candidate.

There were similar allegations in New Mexico, a state which also encountered problems in providing an adequate number of ballot papers — particularly in Republican precincts in one district.

In Ohio, all 12 voting machines in a predominately black district in Cleveland crashed when voting opened at 6.30am, feeding fears that minority — and therefore largely Democrat voters — were being disenfranchised. Election officials in Indiana went to court to get a three-hour voting extension after a computer glitch in 70 precincts delayed poll opening.

Colorado Democrats were opposed by the Republicans when they asked a state judge to allow late voting, arguing that malfunctions had forced long queues to wait up to two hours, while others were turned away. Electronic vote machines were reported to be malfunctioning in Cook County, Illinois, and Lebanon, Pennsylvania. In Madison, Wisconsin, a bomb threat closed a polling station.

Florida’s Broward County, notorious for the “hanging chad” debacle in the 2000 presidential race, had problems as 14 voting machines stopped working for 90 minutes.

In Maryland, Democrat officials accused their opponents of a “conscious, premeditated” campaign of intimidation after it emerged that Republican poll watchers had been issued with a handbook urging them to challenge voters who they suspected of not having the correct paperwork with them.

But in New Jersey it was the Republicans claiming to be victims of a dirty tricks operation with their candidate, Tom Kean, alleging that his campaign headquarters had been padlocked by Democrat operatives. His opponent claimed it was a Republican stunt.

Such name-calling reflected the bitterness with which campaigns across America have been fought in the past two months. According to the independent Centre for Responsive Politics, at least $2.8 billion (£1.5 million) will have been spent by both parties and their allied groups, 20 per cent higher than the 2002 record.

Much of this money has been spent on negative TV adverts. More money has been spent by both parties on get-out-the-vote operations by both parties, which could be critical in midterm elections when turnout is usually low, typically about 40 per cent.

The Democrats need to make net gains of 15 seats to take control of the 435-member House of Representatives for the first time since 1994. To re-take the Senate,they must win at least six seats from 33 being contested.

No results were available when this edition of The Times went to press, although early exit poll information suggested that 62 per cent of voters were motivated by “national issues”, possibly bad news for the Republicans, who had sought to keep the focus away from Iraq and corruption scandals. More bad news was to follow with exit poll returns showing Mr Bush’s approval rate among those surveyed was just 41 per cent with 58 per cent expressing disapproval.

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