Conservative grandee Lord Norman Lamont has thrown his support behind a Brexit ahead of the forthcoming EU referendum. The former Conservative chancellor highlighted high levels of immigration to the UK as a key factor behind his "painful" decision.

"Britain has also lost control of its borders. Of course, we need some immigration, skilled and unskilled, but we do not need immigration in the hundreds of thousands. There is no economic case for it," the peer wrote in The Daily Telegraph.

The 73-year-old also praised David Cameron, saying he "probably got as good a deal from the EU as anyone could" as part of the prime minister's renegotiation. But Lamont warned that the EU would "always push" for further integration, despite Britain's opt-out on the issue.

The former Chancellor went onto hit back at claims that 'leave' campaigners needed to provide a vision of what a post-Brexit agreement with the EU would look like.

"What is forgotten is that the EU needs an agreement just as much as we do. German car manufacturers can't be left up in the air, not knowing the terms on which they can export to their largest market, the UK. There's a mutual need," he declared.

Read more: The who, what, when and why of the historic Brexit vote

Mandelson warns of Brexit 'fantasy'

The comments come after Labour grandee Lord Peter Mandelson claimed anti-EU activists were selling a "fantasy" just months before the 23 June ballot.

"With the fate of future generations and our country's place in the world on the ballot paper it is deeply irresponsible to pretend otherwise," he told the Institute of Chartered Accountants in England and Wales.

Lamont's decision will pit him against the UK's current Conservative chancellor, George Osborne, who recently warned a Brexit would be an "enormous gamble".

But Lord Nigel Lawson, who served as Margaret Thatcher's chancellor, is the chairman of the pro-Brexit Vote Leave campaign.

Lamont, who served under John Major as chancellor between 1990 and 1993, is probably best known in Britain for his role in the Black Wednesday financial crisis.

The UK was forced to embarrassingly pull sterling out of the European Economic and Monetary Union (EMU) in 1992.

Treasury papers released under the Freedom of Information Act in 2005 estimated that the gaffe cost Britain £3.3bn ($4.6bn).