A new study has found that women remain under-represented on ballot papers for the general election.

Research released on Wednesday, conducted by the Fawcett Society campaign group, found that nearly half of all voters will not be able to vote for a woman candidate from one of the three main parties on May 5.

Following the close of nominations last week, in 300 of the 646 constituencies the three main challengers are male.

However the study found that two thirds of the public want to see more women MPs in parliament.

Women are also set to remain vastly under-represented in the Commons following the poll, according to the analysis.

The Conservatives have selected a female candidates in just 12 per cent of their 50 most winnable seats, and the Liberal Democrats 32 per cent.

There was praise for the Labour Party which has selected women in 64 per cent of its top target constituencies and used all-women shortlists in several where sitting MPs have retired.

But where single sex-shortlists were not used Labour was "not much more likely" to field a woman than its rivals, prompting Fawcett to conclude that positive discrimination does work.

"These figures clearly show positive action is the only way for any party significantly to increase its numbers of women MPs," director Dr Katherine Rake said.

"This is also what international evidence has shown.

"MPs make decisions on behalf of the whole country, but currently lack the breadth of experience that a more diverse body of MPs could bring.

"Increasing the proportion of women in parliament should not depend, as it currently does, on the electoral fortunes of one party. It is the responsibility of all parties to play a part.

"Both the Liberal Democrats and the Conservatives must now admit that their well-intentioned attempts to increase their numbers of women MPs without using positive action have failed."