Labour has such large majorities in most seats that even if half of their supporters stayed at home there would still be little chance of change.

The election is a forgone conclusion in eight constituencies, according to the Electoral Reform Society (ERS) which campaigns for a "fairer" voting system.

Labour are in an "invincible" position in Camberwell and Peckham; Dulwich and West Norwood; Lewisham Deptford; Lewisham East; Lewisham West; Streatham; and Vauxhall, while the Liberal Democrats have a similarly safe seat in Southwark North and Bermondsey, says the ERS.

Only Battersea can be seen as the scene of possible change.

The campaign group says candidates in the safe seats were effectively elected from the moment they were confirmed as candidates by their parties.

The ERS says the 43,000 people who voted Conservative in the constituencies in 2001 stood little chance of winning representation, and stand little chance this time around.

"That there is little electoral competition in inner South London is bad for democracy," said ERS chief executive Ken Ritchie.

"When the result of the election is so predictable, the parties have little incentive to campaign and electors little incentive to vote.

"It is not surprise that turnout in some safe seats is extremely low.

"In half of these seats it fell below 50 per cent and in the other four it was only a little higher.

"Turnout ranged from 44.8 per cent in Vauxhall to 53.4 per cent in Dulwich and West Norwood."

The national turnout in 2001 was 58 per cent - the lowest since 1918. It is against this backdrop that Mr Ritchie's group is campaigning for change.

He said: "We are disappointed that there has been so little progress on electoral reform in the last parliament.

"A proportional voting system would make the election competitive in every area and give parties representation according to how many votes they get.

"It would encourage parties to seek votes everywhere, not in just the fortunate few constituencies that happen to be marginal.

"That is why we want a voting system that makes more votes count."