Opinion polls suggest Labour is under extreme pressure from an SNP surge.

The late David Cairns of Labour had a massive majority of 14,416 over the SNP at the 2010 general election on a 63.4 per cent turnout.

Following the death of Mr Cairns, Iain McKenzie retained the Inverclyde seat for Labour in the 2011 by-election, securing a majority of 5,838 over the SNP on a turnout of 45.5 per cent.

Polls have predicted, however, that this could be wiped out today by SNP challenger Ronnie Cowan, the man who led the Yes Inverclyde campaign during last year’s independence referendum.

Labour MPs have represented Greenock since 1936, while the Tories briefly held Renfrewshire West and Inverclyde — which included Port Glasgow — from 1983 to 1987.

But the district seat is now believed to be on a knife edge following last September’s referendum, when the pro-union Better Together camp won by a wafer-thin 86 votes.

Both Labour and the SNP have pulled out all the stops to persuade voters over recent weeks, with each party establishing campaign HQs in Greenock town centre.

Their activists have also been prominent on streets across the area carrying out door-to-door canvassing. Big-hitters have been drafted in to back their respective candidates, with First Minister Nicola Sturgeon drawing a big SNP crowd in Cathcart Square earlier this week and ex-Prime Minister Gordon Brown recently rallying Labour troops on a visit to Greenock.

Celebrities have also been brought in to give their endorsements, with actor Martin Compston joining Mr Cowan on the campaign trail and famous Greenock son Richard Wilson supporting Mr McKenzie.

Now it is time for the voters to deliver their verdict and decide who they will send to Westminster.

There are six contenders for the seat, but polls and bookmakers’ odds suggest that the other candidates — Conservative George Jabbour, who has also fought a high-profile campaign, Lib Dem John Watson, UKIP’s Michael Burrows and Craig Hamilton, of Cannabis is Safer than Alcohol — all face an uphill battle.

Polling stations close at 10pm, when the ballot boxes will be taken to the Waterfront Leisure Centre for counting.

Around 12,500 people opted to vote by post out of a total electorate of 59,000 in Inverclyde, and several thousand of them have already cast their ballots.

Postal votes must be returned by 10pm today. They can be handed in at any polling station up to polls closing, or before 4.45pm at the council’s customer service centre in Clyde Square.

The result is expected to be declared around 3am tomorrow morning. A hung parliament is being predicted, with either Labour or the Tories being forced to form a coalition with other parties in order to form the next UK Government.

See tomorrow’s Telegraph for detailed coverage from the local count, all the reaction to it and the latest on the national results.