Jon WelchNorwich South, one of the most closely-watched constituencies in the country, remained on a knife-edge as the polls closed.Jon Welch

Norwich South, one of the most closely-watched constituencies in the country, remained on a knife-edge as the polls closed.

The constituency has been held by Labour's Charles Clarke since 1997, but he faced a tough fight with the Liberal Democrats, Tories and Greens each claiming to be his main challenger.

The Blairite former Cabinet minister, who has been a persistent critic of Gordon Brown since being relegated to the back benches, was defending a majority of 3,653 and his best hope of survival was that the anti-Clarke vote would be shared out equally between his opponents.

During a final session on the streets to mobilise Labour supporters, he said: 'Turnout seems to be high and our support seems to be holding up well. I'm looking forward to the result later on.'

Turnout in the constituency looks like being high, with queues reported at polling stations, some of which saw as many voters by lunchtime as turned out all day during last year's European elections.

The Green Party, which has turned Norwich into a stronghold in the last few years, has been without an MP at Westminster until now but its deputy leader Adrian Ramsay, a city councillor for seven years, was vying to end that.

With the help of his army of activists dubbed 'Adrian's Army', Mr Ramsay was confident of victory.

'It's been absolutely phenomenal. It's looking like we could win, but I'm not taking anything for granted,' he said.

Liberal Democrat Simon Wright remained the bookies' favourite as the polls closed. Even before his party's Nick Clegg-inspired surge in the polls, he had irked opponents by maintaining only he could unseat Mr Clarke.

'A lot of people have told us they have already voted and I'm encouraged by that. I'm feeling quite positive about the warm response I have had,' he said.

'I still think it's very close. I won't be able to call it until I've witnessed for myself the votes being counted.'

Despite predictions of Conservative gains nationally, Norwich South was unlikely to be among them. Their candidate Antony Little said: 'What's clear to us is Conservatives are voting in large numbers and they are very motivated.

'Large numbers of people who have said they are not going to vote are coming out, and because of that I don't think you can predict the vote.'

The constituency's large student population was predicted to play a decisive role. Natasha Barnes, the Union of UEA Students' communications officer, said: 'There have been queues at the polling station and I don't think it's ever been like this before. Students are definitely voting and could have a huge impact.'