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 listed "key areas of national weakness compared to the rest of the world" during a speech on Britain's future.
Highlighting issues the Conservatives and Labour are divided on, Mr Cameron said the key areas that need changing are Britain's:
- Debt-fuelled, unbalanced economy
- Bloated welfare system
- Under-performing education system
"Fixing these things are the three key domestic priorities of this Government. And though it's taking time, we are making progress and getting our country into shape", he added.
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".
David Cameron said there is "much more to do" to equip the British economy for the modern world and show that we are "back in business".
The Prime Minister said:
We want to go further. The UK is already in the Top 10 countries in the world in which to do business.
In the next three years, we want to see Britain rank up there in the Top 5 places in the world to do business and as the No. 1 country in Europe to do business.
This is about sending the message out loud and clear to international investors, to entrepreneurs at home, Britain is not just getting back in the black - we are getting back in business.
David Cameron said we are in "a battle for Britain's future" ahead of this weekend's G8 summit.
The Prime Minister said the UK must not "hide away from the world" but instead "roll up our sleeves and compete in it".
"It's no use in giving into the world. We must be unashamedly bold and hard-headed about pursuing our national interests", he continued.
"The challenge is clear, we are in a battle for Britain's future".
Prime Minister David Cameron said the mission of his Government is to "turn our country around" and give "all our people the best chance of success".
Mr Cameron said everything the Government is doing has one aim, "To ensure that we build a Britain that is stronger, more prosperous and more full of opportunity for our children".
He said: "I don't serve the British people by sugar-coating the challenges that we face.
"My job is to be upfront about them, to set out what needs to be done, and above all what action we need to take for Britain to succeed".
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.
David Cameron will risk the wrath of Tory backbenchers by making the European Union a key part of his vision for Britain's future.
The Prime Minister is to stress the importance of being at the "top table" in institutions such as the EU, saying membership is in the national interest.
The intervention comes in a speech in Essex tomorrow, billed as setting out the UK's role in the world ahead of the G8 conference in Northern Ireland.
Mr Cameron will argue that the Government is in a "battle for Britain's future", blaming Labour for "passing the buck".
He will acknowledge the pain of austerity, but insist the country has started reforming "just in time" with a "complete plan for national renewal".
David Cameron has paid tribute to the lifeboat crew which helped to rescue dozens of swimmers in Southwold last week.
During Prime Minister's Questions, he said that the RNLI should be treated as an emergency service after Suffolk Coastal MP Therese Coffey asked him to join her in thanking the volunteers.
Hundreds of swimmers got into trouble during the Southwold Pub to Pier swim after the tide suddenly turned.