Obama warned national poll lead is 'misleading'

According to the latest figures, the Democrat is at least seven points ahead of his Republican rival John McCain across the country and appears to be steaming ahead in the key states.

But the final outcome, expected in the early hours of tomorrow, will not necessarily follow the pattern of the polls just as the previous two presidential elections have proved.

In the US, the President is not directly elected in a simple popular vote, because that would encourage candidates to campaign in the big cities and ignore rural states.

Instead, there are effectively 51 separate elections one for each state plus another for the District of Columbia.

Steve Morgan, a Labour strategist who has advised former presidential candidates Al Gore and John Kerry on their campaigns, said the national polls are therefore meaningless in drawing any conclusion about the pattern of a party's likely wins in each state.

He said: "Everybody is looking at national polls and these do not matter. We should be looking at the state by state polls, especially in the key battleground states, like Ohio which could win it or lose it for either candidate."

But he also criticised the individual state polls, saying they do not take into account those who will not admit to pollsters they have no intention of voting for a black man.

He said poll results may suffer from the "Bradley Effect" in which there is an overestimation of support for an African-American candidate because, when race is involved, voters misrepresent their intentions.

"Everybody knows there is a race issue here," said Mr Morgan. "But no one would admit they won't vote for a black person. Even if they just prefer the other candidate, some people would say they are pro-Obama to avoid looking like they are racist. There is definitely an element of polling that is out because of the race issue."

The "Bradley effect" was named after Tom Bradley, the Democratic former mayor of Los Angeles.

He ran for governor of California in 1982 and was expected to win by a wide margin.

In the run-up to the election, polls gave the African-American candidate a lead of between nine and 22 percentage points over his white opponent.

On election day the first exit polls also predicted that he would win, and one newspaper even declared him the victor on its front page.

Mr Bradley lost by more than 100,000 votes. Mr Morgan also said small sample sizes in the US polls could give an inaccurate indication of the final outcome.

"Four years ago, according to the polls, including the exit polls, John Kerry was a clear winner," said Mr Morgan.

"We were so sure about him winning on election day, the Democrats were just about to go on television to announce their policies. It later emerged the polls had all been wrong."

Similarly, in 2000, Democratic candidate Mr Gore was leading in the polls but ended up losing to George Bush.

How the polls stand - click on graphic to enlarge