London: Scotland can become independent from the UK legally and become a member of the European Union within 18 months of voting for independence in March 2016, the Scottish deputy first minister Nicola Sturgeon has said.

If Scotland votes for independence there would be parallel talks with the UK and the European Commission to ensure that Scotland became an independent member of the EU, she said. She insisted the EU would not deny Scotland its right to be members of the EU since this would run counter to the principle of national self-determination, a founding principle of the EU.

Her remarks came after all three parties at Westminster said they would not allow an independent Scotland to remain in a currency union with the rest of the UK and the Commission president Jose Manuel Barroso said it would be difficult if not impossible for Scotland to join the European Union. The two issues threaten to stymie the independence campaign, or at least represent the two biggest stumbling blocks to a Yes Vote this September.

The First Minister Alex Salmond will be addressing the issues in a speech on Monday morning in Aberdeen.

Speaking ahead of the speech Sturgeon told BBC radio 4’s Today programme: “The decision on Scottish independence is for the Scottish people and the decision about continuing membership of the European Union is for the member states. It is a not a decision for the European Commission. What Barroso was saying what that he did not think other members states would want Scotland to continue in membership and therefore it would be very difficult.”

She said no member states, not even Spain, has said they would seek to veto Scotland. It would be enormously disruptive, not just for Scotland, but for the entire European Union for Scotland to be outside the union. It would also be against the founding principles of the EU because Scotland would be effectively being punished for exercising its democratic right to self-determination.”

She conceded Scotland would not seek to change the terms of the existing relationship between the UK and the EU, and said it would not be possible for the EU to force Scotland against its will. She said the European Union cannot force a country into the Euro against its will, pointing to Sweden as a living example.

Similarly she argued Scotland could retain its opt-out from the Schengen border agreement, arguing that the EU is an expansionist institution and would not insist on a border or barrier between Scotland and England. The issue of the rebate would remain unchanged, and its distribution a matter of agreement between England and Scotland after separation.

Sturgeon tried to sidestep the issue of whether the rest of the UK would have to be consulted in a referendum on whether an independent Scotland should remain part of a currency union with the rest of the UK, simply saying it would be in the best interest of the UK for that to happen.

Earlier a distinguished former Judge of the European Court of Justice of the EU Sir David Edward said if Scotland voted for independence, there would be a period of separation between Scotland and the EU. He added: “During that period there is no entity called Scotland that can negotiate with the EU, so the UK would have to negotiate the terms on which the new Scotland at the moment of separation can be a member state or not be a member state.”

He said it was arguable that at moment of separation Scotland would fall out of the European Union with the extraordinary consequence that all its citizens are no longer members of the EU. In addition thousands of commercial relationships would be under a different system of law

He regarded it as grossly optimistic to suggest this negotiation could happen by March 2016, the timetable set out by the SNP.