Prime Minister David Cameron has lashed out at Tory "pessimists" demanding immediate withdrawal from the European Union.
The Prime Minister said he believed it was "possible" to push through changes to the EU.
"I am faced as I do so, if you like, by two groups of pessimists," he said.
"There are some pro-European pessimists who say, 'you have to, in Europe, simply sign up to every single thing that anyone in the EU suggests.
"You sign every treaty, you sign everything - there is no alternative'.
"I think they are completely wrong.
"The second group of pessimists say there is no prospect of reforming the EU, you simply have to leave. I think they are wrong too.
"I think it is possible to change and reform this organisation and change and reform Britain's relationship with it."
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