Scottish independence: William Hague joins Scots-EU debate
Foreign Secretary William Hague has said an independent Scottish state may not be able to negotiate the same terms of EU membership as the UK.
Mr Hague is in Glasgow to unveil the latest UK government paper.
He told BBC Scotland, people "should be in no doubt" that if Scotland left the UK it would have to reapply for European Union membership.
Scottish ministers said the UK government's in/out EU referendum was the real risk to membership.
The Scottish government has argued that, in the event of a "Yes" vote in the 18 September independence referendum, Scotland's EU membership would be negotiated "from within" ahead of its planned "independence day", in March 2016.
Mr Hague told BBC Radio Scotland's Good Morning Scotland programme that, even if the European negotiations were "constructively-minded", it would still be a complicated process involving the agreement of all 28 EU member states.
The foreign secretary said Scotland would be obliged to join the Euro single currency, which the Scottish government had said it would not do.
He also said Scotland would also need to sign the Schengen agreement on border controls, which is "incompatible" with the Common Travel Area plans put forward by the Scottish government.
And Mr Hague further claimed Scotland would lose out on cash from the rebate which the UK gets from the EU.
The Conservative minister said his own party's plans to hold a referendum on EU membership if it was to win next year's UK general election were not an immediate threat.
He said: "I think it is a more immediately, dramatically uncertain world if Scotland were to vote to separate itself from the UK this coming year because what we are trying to achieve by 2017 is a reformed EU that we can recommend the whole of the UK stays in.
"Scotland in effect is going to have two referendums on whether to leave the EU and one of them is in September.
"People should be in no doubt, if part of a member state leaves the EU it has to reapply for membership and that will be a process of uncertain length and unknown outcome in terms of the terms that are negotiated and probably great cost. It means paying more to get less from the EU."
Scotland's deputy first minister, Nicola Sturgeon, told BBC Scotland the UK government's EU referendum, proposed for 2017, posed the only real risk to Scotland's status in the EU.
"The fact of the matter is that, if Scotland votes 'No' and we don't become independent, there is absolutely no guarantee at all that we would stay within the European Union.
"We could find ourselves taken out of it against our will."
Ms Sturgeon added that the Scottish government had clearly set out the route by which Scotland could continue EU membership in its White Paper blueprint for independence.
She also accused Conservative politicians of putting the UK's membership of the EU in doubt, "driven by a fear of UKIP which does not exist in Scotland".