Alex Salmond is considering staying on as a Westminster MP after the next General Election if he becomes Scotland's First Minister, party sources have told The Herald.

The assumption has so far been that if the Nationalist leader were to win a seat at Holyrood on May 3 and become leader of an SNP-led Scottish Executive, then he would stand down as an MP, certainly at the next General Election, still expected to be in the spring or summer of 2009.

However, party sources have pointed out there might be "advantages" to Mr Salmond remaining in the House of Commons beyond the next General Election.

Nationalist thinking appears to be that remaining as an MP would give the party leader a unique weekly platform to raise Scottish issues and goad Prime Minister Gordon Brown, whose premiership - should the SNP form an executive in Edinburgh - could be dogged by "the Scottish question". The 52-year-old 's continued questioning at Westminster set-piece events such as PMQs might not only beleaguer the Labour government but also provide a spur for the Nationalists' key argument: Scottish independence, a referendum on which is likely towards the end of the Scottish parliamentary session in 2010-11.

Moreover, with Mr Salmond as an MP, the SNP's national convener would be able to raise reserved issues such as general taxation, foreign policy, and defence matters in his capacity as Scotland's First Minister in the parliament where the decisions on them are made.

Of course, after 2009 David Cameron could head a Conservative administration in Whitehall, which SNP strategists think would be even likelier to provide ammunition in their campaign against what they deride as London-led government. One sentiment SNP chiefs are keen to encourage in their fight for Scottish independence is English nationalism and there are Tory back benchers who appear more than willing to oblige them.

Mr Salmond's role as the party's star performer was underlined yesterday when the SNP's new campaign image was unveiled: a picture of Mr Salmond with the slogan "First Vote for First Minister".

Launching the image, to be used on billboards, leaflets and websites, Angus Robertson, the party's campaign chief, said: "All the available research tells us more and more Scots believe Alex Salmond is the people's choice for First Minister.

"He stands for success for Scotland and Scottish families and has the fresh ideas to build a healthier, wealthier and safer nation."

The idea of a so-called dual mandate is not new.

After the creation of the Scottish Parliament in 1999, several MPs retained their seats until the General Election in 2001.

While some parties have banned dual mandates as a matter of policy, there is nothing in law to stop them.

SNP high command knows that the thinking towards Mr Salmond retaining his Banff and Buchan seat beyond 2009 is predicated on a broad hypothesis: its leader becoming an MSP; its party winning the highest number of seats in the Scottish Parliament and Mr Salmond retaining his Commons seat at the next General Election.

It is thought if Mr Salmond took up a dual mandate, he would not be entitled to two full parliamentary salaries.

According to the Commons authorities, he would be entitled to his £60,000 Westminster pay plus one-third of his £53,000 MSP's wage.

However, as First Minister he would also be entitled to a ministerial salary of £75,000, which would bring his overall pay packet to £153,000.

Yet, the intriguing prospect of the Nationalist leader remaining on the Commons green benches beyond 2009 will undoubtedly raise a few eyebrows, not least those of the Chancellor and Prime Minister-in-waiting.

Today, in Glasgow, Mr Salmond will announce his party's new business campaign at a visit to launch the offices of Conscia, a pioneering web and mobile applications development group.