Phil Bennion has warned David Cameron not to play Russian roulette with Britain's European future in an effort to satisfy rightwingers in his party.
The West Midlands MEP urged the Prime Minister to listen to the business community and security experts, not his more fanatic backbench MPs, in his delayed speech on Europe.
Phil Bennion commented:
"The speculation before this speech has already been very damaging for Britain's reputation in the EU. The expectations being ramped up about this speech among fanatic Tory eurosceptics are extremely dangerous.
"One in ten UK jobs - probably a lot more than that in this region, depend on our trade with and membership of the European Single Market.
"The huge recent growth at Jaguar Land Rover for instance is in part because of the UK position with Europe as a cornerstone of our economy.
"Leaving the EU would be catastrophic for Britain, cut us off from our key markets and reduce our influence in the world.
"David Cameron must not talk up threats of Britain leaving the EU as some kind of negotiating tactic. He risks playing Russian roulette with our future and doing terrible damage to businesses trying to get us out of the recession and increase our exports.
"He needs to show some courage to face down his eurosceptics and do what is right for Britain, not what is convenient to satisfy the right of the Conservative party."
On the potential opt out of EU justice and home affairs policies, he added:
"Any security expert will tell you that we have to work together across borders to tackle serious crime such as illicit drugs, human trafficking or international paedophile rings. If we don't, we risk becoming a safe haven for criminals.
"Climate change is another massive threat to us, but doesn't stop at the white cliffs of Dover.
"Cameron has allowed himself to be boxed into a corner by the europhobes in his party. This speech has to be constructive. Gambling on our European economic future to satisfy little Englanders could be disastrous and he must not do it."
Note to Editors
A recent opinion poll by YouGov/Sunday Times revealed that by a 40% to 9% margin, respondents thought that the UK would have less influence in the world if it left the European Union.