Mr Hague said Scotland benefited enormously from the union but warned that voting in favour of independence would mean splitting from the world organisations the UK had signed up to.
He said: “Scotland, of course, derives enormous benefit from being part of the United Kingdom. And the United Kingdom benefits enormously from Scotland being part of the United Kingdom.
“It is very important to understand that if Scotland left the United Kingdom, it would also be leaving the organisations the United Kingdom is a member of, including the European Union.”
His comments followed a question from Graeme Morrice (Livingston), who said: “What assessment have you made on an independent Scotland’s place in Europe and the world compared to the advantage Scotland derives currently from being part of a strong United Kingdom?”