THE race to be Deputy First Minister to Nicola Sturgeon, who is favourite to become the next SNP leader and Scotland's leading politician, is wide open.

Transport Minister Keith Brown and Westminster Treasury Minister Stewart Hosie are leading contenders for the post, but Local Government Minister Derek Mackay has ruled himself out.

Mr Brown has been a success story in the transport portfolio but above all has a back story as a former marine who served in the Falklands.

Mr Hosie is Treasury spokesman, a key battleground over coming years.

He is partner of Sports Minister Shona Robison, who is close to Ms Sturgeon.

Party members will decide on the strength of the next battle to come when they meet in November to settle the issues at annual conference in Perth.

Last night, there were still no official challengers for the post which is technically the deputy national convener of the Scottish National Party, but it is bound to be contested heavily in the weeks to come as the top job is seen as a given.

Ms Sturgeon will close the two-day Holyrood debate on the referendum tomorrow night but by that time she will already be settling in to the role of future boss of her party and her country.

It follows First Minister and SNP leader Alex Salmond's announcement in the wake of losing the referendum battle on Friday that he is to quit.

No-one is standing for the national convener post against Ms Sturgeon and that is likely to remain the case.

All of the party heavyweights occupying Cabinet positions have agreed Ms Sturgeon is the woman for the job, especially as "her mentor" Mr Salmond is backing her.

Much more attention is now focused on Ms Sturgeon's current post of SNP deputy leader and Deputy First Minister.

Ms Sturgeon will launch her formal campaign within days, but the election for her successor as deputy will see a proper power battle between MSPs, MPs and even MEPs.

There is an argument that Westminster should provide the deputy leader.

But MEP Alyn Smith has said he may throw his hat in the ring, arguing that at times the Holyrood-dominated thinking of the party neglects the grass roots.

In April, Mr Smith stunned an audience during a speech when he claimed the leadership had not listened to his advice on EU membership in the event of independence.

He said that it would not be as automatic as had been suggested.

Angus Robertson is the current Westminster leader but he led the change in SNP policy towards Nato membership and might struggle for support among the party grassroots.

That Nato decision saw well-liked radical MSPs resign from the party, and sucking up to Nato did not win a referendum anyway. Watch for a backlash there.

All his strategy work for the party could well see a rough and unfair return.

If the party goes for Holyrood talent then there are, realistically, a handful of contenders once all the big beasts such as Health Secretary Alex Neil and Education Secretary Michael Russell have ruled themselves out.

One of the SNP's historic problems has been how to go about spreading its word beyond its heartland.

That used to be code for East Coast bias. No longer. Since Glasgow voted Yes there will remain a strong need to keep the East Coast on-side, with Edinburgh having voted No in Thursday's poll.

It is understood a Sturgeon leadership, rooted in Glasgow voting Yes last week, may want a bit of geographical ballast.

Party sources also say there are only two routes to follow.

One is to accept that the next Westminster Election is the next great contest and an MP would be an asset as deputy leader.

In those circumstances it becomes a contest between Angus Robertson, the Westminster group leader, and his Treasury spokesman Stewart Hosie.

The other is to say that Holyrood remains the main focus and First Minister Sturgeon will want a proper Holyrood number two.

Today, the Scottish Parliament will reconvene for the first time since the independence referendum. One of the first items of business will be a statement from Mr Salmond, in which he is expected to formally announce his plans to resign to the chamber.