THE president of the European Parliament has blocked legal advice on whether an independent Scotland could be fast-tracked to EU membership.

Martin Schulz personally intervened to stop publication of the opinion - sought by Labour and UKIP members - because he feared it could amount to "interference" in the independence debate.

The German Social Democrat wields huge power in Strasbourg as parliament president and, despite British Labour opposition, is also a leading candidate to replace current Commission President, Jose Manuel Barroso.

His intervention means it is now unlikely that there will be any formal opinion expressed by any European Union institution on membership for Scotland - or Catalonia, which will also hold an independence vote later this year.

As The Herald revealed last month, the European Parliament's Committee on Constitutional Affairs had commissioned an opinion from its own lawyers on how Scotland could go about rejoining the EU.

Legal experts were due to report back to the committee later this month in what would have been the biggest test yet of the SNP view - shared by some experts but also rejected by others - that an independent Scotland could seamlessly join Europe in a quick treaty amendment.

Mr Schulz, however, told committee chairman Carlo Casini such a report "might create interferences with the on-going Scottish referendum campaign" and was "not appropriate for the time being".

Mr Casini's committee sought the opinion after pressure from two Scottish Labour MEPs Catherine Stihler and David Martin.

A UKIP MEP - climate-change denier Stuart Agnew - had volunteered to write a "non-partisan" report on the issue for the committee after declaring the Scottish Government's White Paper to be "misleading" on EU membership.

Mr Agnew's assistant, in an email seen by The Herald, said: "It must be assumed, in the light of remarks made by Mr Barroso, that much of the legal groundwork has already been done by the Commission and a report could be produced very rapidly."

Several prominent officials in EU institutions, including Mr Barroso, have made what Scottish nationalists regard as unhelpful noises in recent months. Pro-UK sources had hoped the parliamentary opinion would go against the SNP's view.

Ian Hudghton MEP, the party's president, last night said: "Clearly the Labour MEPs who keep hoping that EU institutions will take the side of the No campaign will be disappointed."