Theresa May's once formidable lead has been eroded though her Conservative Party could still be on course to win a majority of seats in parliament, an opinion poll and an electoral model showed on Friday.

With less than a week before polling day on Thursday, May's Conservatives now lead the opposition Labour Party by just five percentage points, down from 15 just over two weeks ago, according to the survey from Ipsos MORI.

The Ipsos MORI poll put the Conservatives on 45 percent, down four points from a comparable survey on May 18, with Labour up 6 points to 40 percent.

'It is clear that on contact with the voters, Mrs May is not going down well and she is losing ground in particular amongst middle aged voters and female voters,' Ben Page, chief executive of Ipsos MORI, told Reuters.

Page said that Labour's share of the vote included many younger voters who had not voted before.

'Even with all those young people who say they are going to vote and may not, Mrs May should still win a majority so I wouldn't sell your pounds yet,' Page said.

The findings echo other recent polls which show May's once commanding lead of more than 20 points when she called the campaign being whittled away, meaning she might no longer win the landslide she hoped.

A respected model made by Michael Ashcroft, who once served as treasurer of the Conservative Party, showed on Friday that May's likely majority had declined from a week ago but estimated that she would still increase her majority to 60 seats.

A failure to win the June 8 election with a large majority would weaken May just as Brexit talks are due to begin while the loss of her majority would pitch British politics into turmoil.

Against the Bank of England's trade-weighted basket, which measures sterling's broader strength, the pound is now back where it was on April 9, before May called the election.

May, who won the top job in the political chaos following the shock June 23 Brexit vote, had hoped the election would strengthen her hand ahead of Brexit negotiations, and the party was expected to take advantage of the apparent weakness and disarray of its main rival.

However, Labour leader Jeremy Corbyn, a 68-year-old socialist peace campaigner, has been pulling big crowds at rallies across the country, brushing off warnings from opponents in his own party that he would lead them to electoral disaster.

In a further blow to the Conservatives on Friday, one of its candidates who beat leading Brexit figure Nigel Farage in the 2015 parliamentary election, was charged with breaking expenses rules during that campaign.