The British and Scottish governments on Monday signed a historic deal that will to allow Scotland to hold a referendum in 2014 on whether it wants to remain part of the United Kingdom or secede from the 300-year-old political union.

Under the terms of the agreement signed by Prime Minister David Cameron and Scotland’s First Minister and the leader of the ruling Scottish National Party (SNP) Alex Salmond in Edinburgh, voters will be asked to say “yes” or “no” to a single question: whether they want an independent Scotland?

The voting age will be reduced to 16.

Mr. Cameron’s Conservative Party and the two other mainstream national parties — Labour and the Liberal Democrats — will campaign for a “No” vote.

The agreement was criticised by unionists who accused Mr. Cameron of “surrendering” to the SNP. He defended it saying that he wanted to “show respect to the people of Scotland”, who had voted for a party that wanted a referendum. But he insisted that Scotland would be “better off” with the U.K.

“I passionately believe Scotland will be better off in the United Kingdom but also, crucially, the United Kingdom will be better off with Scotland,” he said as he shook hands with Mr. Salmond.

Mr. Salmond described it as a “historic day” for Scotland and “a major step forward in Scotland’s home rule journey”.

Public support for an independent Scotland remains low.

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