NICOLA Sturgeon yesterday urged female voters to put their trust in the SNP and shatter the glass ceiling, as Labour tried to reach women by stoking fears of a second independence referendum.

As the SNP and Labour set out their key messages for the last full week of election campaign, the First Minister launched a Women's Pledge promising equality in pay, education and health, and action against domestic abuse.

While former PM Gordon Brown warned the SNP would use victory on May 7 to force a second referendum - a message the party hopes will resonate with female voters.

The most recent Scottish poll showed SNP support among women lagging six points behind support among men.

Women were also less likely to vote Yes in last year's referendum than men, although the gender gap narrowed to just three points by polling day.

With Scottish Labour facing a wipeout at the hands of the SNP, Brown made it clear the party would now focus on a referendum as its main line of attack.

Speaking in Renfrewshire in support of Labour's Douglas Alexander, Brown homed in on Alexander's 20-year-old SNP rival, Mhairi Black, who is ahead in the polls.

In a video, Black had said a large number of SNP MPs would be able to "twist the arm" of other Westminster parties "to get that other referendum".

Brown said: "Remember what the SNP used to say - the referendum was once in a generation, then it changed a little to once in a lifetime, then it was once every 15 years and now when you ask Ms Sturgeon about this her answers are all evasion. She cannot give a straight answer to the question.

"But does not the SNP candidate in this constituency tell the truth, that what they want is an SNP vote not to deliver social justice but to deliver the chaos and constitutional crisis at Westminster to as she said force a second referendum?

"I don't want the divisiveness, I don't want the bitterness, I don't want the acrimony, I don't want the divisions between families and communities in the next few months that we had in the past few months."

Scottish Labour leader Jim Murphy will repeat the warning about a second referendum in Edinburgh today.

Deputy First Minister John Swinney said Gordon Brown seemed to be "re-fighting last year's referendum" while the SNP were out talking to voters about the future.

In a tacit rebuttal of the developing Labour line of attack, the SNP went out of its way to sell itself to female voters by promising more free childcare, an end to the gender pay gap and 50-50 gender balance in the boardroom by 2020.

The party also said it would invest in women through continuing free education and apprenticeships, protect child benefit, carer's allowance and child tax credits, and "ensure that no girl grows up or woman lives in fear of abuse and violence".

At a gathering of 1000 women in Glasgow city centre, Sturgeon said: "No young girl should grow up in 2015 with the prospect of facing a glass ceiling that limits their ambitions. We owe it to future generations to end gender inequality once and for all.

"Westminster's austerity cuts have hit women the hardest of all, with 85 per cent of cuts to social security and pensions affecting the incomes of women.

"That is wholly unfair and only undermines progress on gender equality, yet Labour is committed to a further £30bn of austerity.

"SNP MPs at Westminster will stand up for gender equality at every turn. We will work for an end to austerity, for equal pay, more and better jobs and to end the barriers that still block the aspirations of too many women in Scotland and across the UK."

UK LibDem leader Nick Clegg, who faces a Tory takeover of LibDems seats in the South West, distanced himself from the SNP, saying he could not support a Labour government that relied on Nationalist "life support".

Appearing to show his preference for another LibDem-Con coalition, Clegg said voters would question the "birthright" of a Labour government formed with fewer MPs than the Tories.

"I totally rule out any arrangements with the SNP. I would never recommend to the Liberal Democrats that we help establish a government which is basically on a life support system, where Alex Salmond could pull the plug any time he wants. No, no, no."

In another interview, Sturgeon she said she expected SNP MPs to wield "enormous influence" over Labour.

David Cameron predicted the first black or Asian Prime Minister would be a Tory.

Setting out plans for more ethnic minority candidates, he said: "We are the first party to have a female prime minister, we were the party of the first Jewish prime minister and I know one day we are going to be the party of the first black or Asian prime minister."

He refused to comment on reports that London Mayor Boris Johnson is being lined up for a swift "coronation" as next Tory leader if Cameron fails to win a majority.

Ukip leader Nigel Farage admitted he had not been "firing on all cylinders" due to treatment for a back injury sustained in a light aircraft crash on polling day in 2010.

A UK-wide YouGov poll found Labour maintaining a two-point lead on 35% to the Conservatives' 33%, with Ukip on 13%, Liberal Democrats on 8% and Greens on 6%.