Eurosceptic Tory backbencher Bernard Jenkin said Brits "cannot afford to be 'little Europeans'" following David Cameron's speech on Britain's future.
Mr Jenkin said: "The Prime Minister has come to Essex to warn that we cannot afford to be 'little Englanders' - and he is right - but we cannot afford to be 'little Europeans' either, but that's where the EU is taking the UK.
"He is right that the UK's prosperity and security depend so much on what happens in the rest of the world, but wrong to suggest that the UK must stay in the EU.
"Unless there is a fundamental change in our relationship with the EU, the UK will simply have to leave the EU, so British business is free to compete".
Prime Minister David Cameron said membership of international organisations such as NATO, the United Nations and the EU is "not a national vanity - it is in our national interest".
Mr Cameron highlighted that Britain's prosperity depends on international ties and global trade.
He said: "This country depends for its living on international ties and global trade. They in turn depend on global stability and security, and on there being global rules to abide by.
"When your prosperity is won in far flung places, when your fortunes are disproportionately affected by what goes on beyond your borders, then your national interest is not just about standing up for yourself - but standing up for what's right.
"Fortune favours Britain when we're ambitious, when we count, we play our part in the world".
Prime Minister David Cameron will today insist he has a "very clear vision" of the country he wants to live in, where everyone has opportunities.
Turning to Britain's connections abroad, the Prime Minister will make an apparent reference to his pledge of an in-out EU referendum if the Tories win the general election, saying his policy on the issue is "clear".
But he will also echo one of the most common arguments deployed by supporters of EU membership.
"This country depends for its living on international ties and global trade," he is to say. "They in turn depend on global stability and security. And on there being global rules to abide by.
In a speech today, Prime Minister David Cameron will establish key dividing lines with Labour over policy and the direction of the coalition government.
He is to say:
We have identified, very clearly, our key areas of national weakness compared to the rest of the world.
One - our debt-fuelled, unbalanced economy. Two - our bloated welfare system. Three - our under-performing education system.
These are the priorities that define and drive our domestic agenda. A stronger economy. Welfare that works. A world-class education system. And we are pursuing them with ruthless ambition for everyone in this country.
Mr Cameron will cite changes to the planning system, the welfare shake-up and restrictions on non-EU migration among the coalition's achievements.