The union is "greater than the sum of its parts," Hague said in a speech Friday in Glasgow, announcing a UK government analysis of the potential impact of Scottish secession on foreign affairs. The Conservative foreign minister also called unlikely the Scottish government's claim that it could engineer a "seamless transition" to full membership in the European Union.

"I feel deeply that what is at stake this year is not only Scotland's future but all our future, because Scotland leaving the United Kingdom would diminish us all," Hague said.

Hague warned that European Commission President Jose Manuel Barroso and European Council President Herman Van Rompuy have indicated that Scotland would have to reapply for EU membership. He said that should the independent Scotland succeed in rejoining the EU, it may have to adopt the euro as its currency and join the passport-free Schengen zone, which allows for seamless travel between most countries in the bloc - with the exception of the United Kingdom. Independence advocates say they want to keep the pound as the country's currency and remain in the EU and NATO if the country votes to separate.

'Hypocritical Tories'

Voters will make their decision on September 18. Independence would take effect in March 2016.

Scotland's deputy first minister, Nicola Sturgeon, rejected Hague's arguments as "an example of the same old hypocritical Tories lecturing Scotland on why we shouldn't be taking decisions ourselves." Sturgeon, the second in command to Alex Salmond of the Scottish National Party, added that a proposed referendum on UK's leaving the European Union "could see Scotland out of the EU even if we vote to stay in."

"More than ever Scotland needs direct representation in Europe so we can protect and promote Scotland's interests," said Sturgeon, who also wrote an open letter to Hague challenging him to answer 12 questions about the analysis he presented on Friday.

Among the country's four main parties, the Scottish National Party has campaigned for independence. The Conservatives, Labour and the Liberal Democrats oppose the measure. Opinion polls show that the independence movement has the support of only a third of voters, but anti-separatist campaigners have warned against complacency as about 15 percent of Scots remain undecided.

mkg/dr (Reuters, AFP, dpa, AP)