By Nyta Mann BBC News Online political correspondent

The government has sought to do something about its women trouble - specifically, the problem of under-representation within Labour's parliamentary ranks of female MPs.

Ministers have published their proposals to change the 1975 Sex Discrimination Act to allow political parties to positively discriminate in favour of women candidates.

Of the 659 MPs that make up the House of Commons, only 118 are women - a step backwards from 1997, which saw 120 women among the parliamentary intake.

That 1997 progress was largely a result of Labour's use ahead of its first landslide of all-women shortlists for parliamentary selections.

The policy proved highly controversial within the party, and was eventually judged unlawful by an industrial tribunal, but it succeeded in sending a record-breaking number of women to Westminster.

During last June's general election Labour promised it would take concrete steps to reform the law.

Contentious

MPs are expected to debate the short bill, which is just four clauses long, before the end of October.

It will not impose mandatory all-women shortlists, so it will be entirely up to the political parties whether they wish to take advantage of its measures.

All the main political parties agree they need more women MPs. How to actually go about getting them has proved highly contentious, however.

Last week new Conservative leader Iain Duncan Smith used his conference speech to talk of the desirability for "greater opportunity" for women within the Tory Party.

But he has ruled out all-women shortlists and no other measures are proposed.

And last month, the Liberal Democrat party conference voted down the leadership to reject moves to boost its own number of women candidates.

Limited life-span

The government, 95 of whose 413 MPs are women, will undoubtedly seek to embarrass the opposition parties with the bill - particularly the Conservatives, who have 14 women MPs out of a total 166, and who have denounced: Labour's positive discrimination as politically correct quotas.

By introducing the bill this early in the parliamentary session, political parties can put it into operation ready for the start of the long process of parliamentary selections ahead of the next general election.

And in consideration that the proposed new law is a measure very much tied to the particular circumstances of the present, it includes a time-limiting "sunset clause".

The effect of this is that if passed, the new laws will only have a life up to 2015 - though parliament can choose to renew it if it so wishes.

Labour MP Joan Ruddock has been part of an ongoing campaign to boost the number of female MPs.

She said: "The government's legislation will amend the Sex Discrimination Act so that fear of legal challenge is removed from political parties that choose to adopt positive measures, such as all-women shortlists, in selection.

"This is a complete vindication for all of us who have argued that only a return to all-women shortlists could raise the number of women selected at Westminster."