All-women shortlists are the only way to ensure more female Conservative MPs, a former shadow cabinet minister has said.

In an article for Wednesday's Independent, Mr Bercow said the "dearth of women MPs on the Conservative benches makes us look narrow, prejudiced and unrepresentative of the country we seek to govern".

But he said enlarging the number of would-be female candidates alone would not guarantee an increase in the number being selected for winnable seats.

The former right winger quit as shadow pensions minister last year over Mr Duncan Smith's opposition to child adoption by homosexuals.

Traditionalist anger

His comments are clearly designed to increase the pressure on party chairman Theresa May, who has pledged to greatly increase the number of women MPs.

Mrs May has called on local Conservative Associations to select more women as prospective parliamentary candidates.

She has not ruled out introducing a quota system if they fail to comply.

But of the 60 candidates chosen so far in target seats, only seven are women.

Any move towards positive discrimination is likely to enrage the traditionalist wing of the party.

In his article, Mr Bercow said: "For at least 10 years, every Conservative responsible for candidates has talked enthusiastically about the need for more women MPs and his or her resolve to recruit them.

"Despite this, it simply has not happened."

Shortlist options

He concluded: "We have two credible options.

"One is to impose all-women shortlists for, say, 50 per cent of marginal seats we need to win and Conservative seats with a vacancy to fill.

"The other is to produce for winnable seats a new, shorter list of candidates, half of whom would be women.

"I am sure that the latter, excellent idea will appeal to Theresa May.

"After all, in July 2001, she proposed it."

Leadership attacked

Mr Bercow has become increasingly critical of his party's leadership since walking out of the shadow cabinet.

Speaking on GMTV at the weekend, he said party leader Iain Duncan Smith was in "considerable trouble".

"Our chance of winning the next general election is about as great as that of finding an Eskimo in the desert," he added.