(Reuters) - British opposition Labour party leader Ed Miliband's approval rating has hit a record low, a poll showed on Sunday, raising further doubts about his ability to unseat Prime Minister David Cameron in a national election in just over six months.

The survey was published after polling data last week showed Miliband's left-leaning party was set to be nearly wiped out in Scotland, a traditional stronghold, and after a string of polls suggested a long UK-wide lead it had enjoyed over Cameron's Conservatives has shrunk.

Derided by the press as socially awkward since he assumed the party's leadership in 2010, Miliband, an Oxford-educated career politician with the demeanor of an academic, is seen by some in and around his party as an electoral liability rather than an asset.

Sunday's poll, by YouGov for The Sunday Times newspaper, showed that 73 percent of voters thought Miliband, 44, was doing badly, with only 18 percent saying he was doing a good job. That gave him an overall approval rating of -55.

Last month, Miliband's rating hit a 33-month low in a comparable YouGov poll, with 71 percent saying he was doing badly and 20 percent well. His latest approval rating means he has overtaken Nick Clegg, the deputy prime minister and leader of the Liberal Democrats, as the least popular of the three main party leaders.

Labour's overall support was 32 percent, the same poll said, just one point ahead of the Conservatives, its lowest level of support since 2010.

Cameron, the 48-year-old leader of the Conservative party, remains the most popular of the party leaders, the poll showed, with 54 percent saying he was doing his job badly and 40 percent well. That gave him an approval rating of -14.

Yvette Cooper, Labour's spokeswoman for home affairs, said on Sunday she thought Miliband was doing a good job, but John Prescott, Labour's former deputy prime minister, suggested there were problems with strategy.

"To be frank, our campaigns have not been very successful," Prescott wrote in the Sunday Mirror newspaper.

"From the 2010 general election to local and European elections and by-elections, it seems strategy is driven by the pointy-heads not the lionhearts. In these last six months we need passionate campaigners to sell our popular policies."

Miliband, the main challenger to Cameron for the top job in British politics, has long been troubled by what he has dismissed as a superficial image problem with his policies at times overshadowed by perceived presentational shortcomings.

He has also struggled to completely win over his own lawmakers, a majority of whom voted for his brother David in a leadership contest in 2010, and has come under criticism from party members in northern England who have accused him of shying away from difficult issues such as immigration.

In an embarrassing slip, Miliband, who was speaking without notes, forgot vital chunks of his own speech to his party's conference in September that touched on Britain's sizeable public deficit and immigration.

Sunday's poll was conducted from Oct. 30-31 among 1,808 British adults.