The Prime Minister David Cameron said the eurozone debt crisis presents an opportunity to reform the European Union and for powers to "ebb back" from Brussels to Westminster.
In a speech in the City of London last night, Cameron said it would not be in the UK's interests to exit the union, but that it may now be in a position to renegotiate its membership.
A number of Conservatives want the UK to leave the EU altogether and, last month, 81 Tory MPs voted in favour of a referendum on the UK's place in the union.
Cameron said the EU is too often seen as an "abstract end in itself" and detached from economic reality.
He said the UK and the other 26 member states needed a more "outward looking", "flexible" and "diverse" union.
"We have a right to ask what the European Union should and should not do and change it accordingly," he said.
"Change brings opportunities. An opportunity to begin to refashion the EU so it better serves this nation's interests and the interests of its other 26 nations.
"An opportunity, in Britain's case, for powers to ebb back instead of flow away and for the European Union to focus on what really matters to underpin prosperity, stability and growth.
"That is the kind of fundamental reform I yearn for."
Cameron said he believed Europe was "slipping behind" other economic powers and that, unless it becomes more competitive, it will remain a "continent in trouble".
But he said the UK has more powers as part of the EU than as a standalone nation.
"Leaving the EU is not in our national interest," he will argue. "Outside, we would end up like Norway, subject to every rule for the single market made in Brussels but unable to shape those rules.
"Believe me, if we weren't in there helping write the rules they would be written without us - the biggest supporter of open markets and free trade - and we would not like the outcome."
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