DAVID Cameron has explicitly denied he would resign as Prime Minister if Scotland voted for independence in September, rebuffing suggestions from some of his own ­Conservative colleagues that he would have to stand down if he lost the Union.

The Prime Minister's insistence came as Lord Wallace, his Liberal Democrat colleague, eschewed any sense of negativity when promoting the benefits of the UK passport, without even mentioning the issue of Scottish independence.

Mr Cameron was asked again if he would resign if the pro-UK campaign lost the referendum battle. "No," he replied, "and it is very important people understand that because it is not my name or anyone else's name on the ballot paper." Recently, one unnamed ministerial colleague claimed it would be very difficult for the PM not to stand down after a Yes vote "because he would go down in history as the Prime Minister who lost the Union".

Pointing to his promise that any future Conservative government at Westminster would back more powers for Holyrood, Mr Cameron said once the independence question had been settled, "then you can properly engage with future acts of devolution on which, I have a pretty good track record".

He added: "We have a massive act of devolution coming through right now giving the Scottish Parliament far more power to spend money as it chooses."

A spokesman for Alex Salmond said: "What Mr Cameron does the day after a Yes vote in September is entirely up to him. In the meantime, he should step up to the plate and agree to a head-to-head debate with the First Minister, as he will find it very difficult to defend his position if he has not come out to bat for his side," he added. Elsewhere, on a visit to HM Passport Office in Glasgow, Lord Wallace, the Advocate General, hailed the UK passport as "one of the most trusted and secure documents in the world".