FOREIGN Secretary William Hague has challenged Alex Salmond to offer voters "clarity" on the key European issues an independent Scotland would face as the First Minister makes a major speech in Bruges today.

Mr Salmond will make the case that an independent Scotland would be an enthusiastic lynchpin of the EU sharing and promoting the "solidarity, freedom and democracy that are the heart of the European project".

The medieval city provided the backdrop for Prime Minister Margaret Thatcher to outline her concerns about the future direction of European policy in 1988.

Ahead of Mr Salmond's speech to the College of Europe, Mr Hague in a letter to the SNP called on him to offer "clarity on a number of key issues, (on) which voters in September's referendum need better information".

He said these included whether all EU member states had agreed to the SNP's proposed accession process, and what Plan B an independent Scotland would have if it failed to meet Mr Salmond's 18-month deadline for negotiations.

Mr Salmond told Mr Hague the proposed accession mechanism is supported by "many experts" , while the 18-month timetable was described as "realistic" by a Coalition adviser Professor James Crawford.

He added: "In this, as in much other in this debate, a positive vision is proving far more powerful than the depressing negativity of the London approach."

Over the weekend the Liberal Democrat Chief Secretary to the Treasury, Danny Alexander, ahead of a speech later this week, also called on the Scottish Government to produce its own "realistic analysis of the cost of independence" as he attacked what he said were unrealistic assumptions about North Sea Oil revenue.

Meanwhile, in his most high-profile intervention in the debate, John Reid, former Labour defence secretary accused the SNP of being engaged in a "cruel deceit".

However, Bernard Savage, a diplomat in the EU's European External Action Service, directing relations between the EU and North Africa, and Yes supporters, said: "Mr Salmond is winning the argument."