A major Conservative donor has said the UK has "nothing to fear" from leaving the European Union and criticised David Cameron for keeping the country "in the dark" over his renegotiation of the relationship with Brussels.
JCB chairman Lord Bamford said the price of membership "has simply become too high" and that he would vote to leave unless the Prime Minister secured "truly radical reform".
Writing in the Daily Telegraph, the peer said he had voted to remain in the then European Economic Community the last time the country voted, in 1975, because it "would be good for business and good for Britain".
But he said the "intrusion" of the EU into more areas of national responsibility, an "out of hand" net annual subscription, and a "less business-friendly" environment had swung the case the other way.
"We hear a lot about the risks of leaving the EU, but we do not hear enough about the risks of staying in," he wrote.
"We do not have enough sovereign control over our own affairs now but will we have still less in the future? We are over-regulated now but will it become even more onerous?"
Calling for more "opt-outs of similar magnitude" to those that saw the UK remain outside the Schengen borderless area and the eurozone, he welcomed the leading role in negotiations handed to "astute" Chancellor George Osbone.
But he went on: "My main concern is that we're being kept in the dark on the negotiations,
"Keeping us in the dark is not helping the Government, in my view, nor will it help convince the public when the referendum comes around.
"The Prime Minister has stated that he is seeking proper full-on treaty change and a fundamental change in Britain's relationship with the EU.
"I applaud his ambition and sincerely wish him well but I do believe we're entitled to greater transparency. We need to see some real detail."
He went on: "If the Government fails to secure truly radical reform, I will have no other choice but to vote to leave.
"Let me be clear: Britain's exit from the EU is not my preferred option, but if that's what happens, so be it. If the choice of the British people is to leave, we have nothing to fear but fear itself."
His intervention came after Lloyds Baking Group chairman Lord Blackwell said that without major reforms, there were no "compelling economic arguments" for the UK not to withdraw.
The former adviser to Sir John Major and Baroness Thatcher told the House of Lords membership was not "ultimately sustainable" without a "significant change in the current arrangements".