DAVID Cameron has warned that leaving the EU would be the "self-destruct option" for Britain as the Treasury published analysis warning that Brexit would plunge the country into a year-long recession and cost as many as 820,000 jobs.

Speaking at the B&Q HQ in Hampshire, the Prime Minister said a Leave vote would create the world's first "DIY recession" as the country inflicted economic harm on itself just as it was recovering from the crash of 2008.

And he said the threat to families' financial security and the nation's economy meant that a Remain vote was the "moral" choice in the referendum, exactly a month away on June 23.

The Leave camp claimed the Treasury’s doom-laden forecasts were more scaremongering and leading Outer, Iain Duncan Smith, the former Work and Pensions Secretary, said the warnings "should not be believed by anyone" as the analysis was "not an honest assessment but a deeply biased view of the future".

The Scot pointed out there was "not one word about the risks of remaining" in the UK Government analysis; by ignoring this, he argued, the Government was "misusing its power and misusing the civil service".

The new Treasury analysis of the short-term impact of withdrawal from the EU suggested that between 520,000 and 820,000 jobs would be lost while house prices would fall by between 10 per cent and 18 per cent. Public sector borrowing would rocket by between £24 billion and £39bn,

Mr Cameron said Britain was now "back on the right track" after the financial crisis and urged voters not to put that at risk.

"As the Bank of England has said and the IMF has underlined, and the Treasury has now confirmed, the shock to our economy after leaving Europe would tip the country into recession. This could be, for the first time in history, a recession brought on ourselves. As I stand here in B&Q, it would be a DIY recession," he declared.

Standing alongside the PM, Chancellor George Osborne urged wavering voters to consider whether they were ready to "knowingly vote for recession".

In a rebuff to Leave campaigners who suggest that some economic pain is "a price worth paying" for winning back sovereignty from Brussels, Mr Osborne said: "It's not your wages that will be hit, it's not your livelihoods that will go, it's not you who will struggle to pay the bills; it's the working people of Britain who will pay the price if we leave the EU."

Mr Cameron rejected the idea that a "moral" case for Brexit might trump economic concerns.

"The economic case is the moral case," he insisted. "The moral case for keeping parents in work, firms in business, the pound in health, Britain in credit, the moral case for providing economic opportunity rather than unemployment for the next generation.

"Where is the morality in putting any of that at risk for some unknown end?"

After six years of austerity, Britain now had a lower deficit, a growing economy and increasing numbers of jobs, said Mr Cameron.

And he asked: "After all the pain, all the sacrifice by the British people, why would we want to put it at risk again? It would be like surviving a fall and then running straight back to the cliff-edge. It is the self-destruct option."

Mr Cameron singled out Ukip leader Nigel Farage as he rejected the stance of Brexit campaigners who viewed the economic cost as a price worth paying for getting out of the EU.

"There are people out there who say yes, there would be a hit to our economy but it is somehow worth it for other reasons; I have heard Nigel Farage, for instance, say that many times.

"I profoundly disagree. Particularly because we have this special status within the EU - we are not in the euro, we are not in the no-borders zone, we are out of 'ever closer union' - we have a special deal in Europe and with that in mind it is certainly not worth the huge risk and downside to our economy of voting to leave."

The PM said the Treasury predictions were not a "radical" surprise and denied that it was a "DIY forecast".

He said: "This comes after very similar warnings from a number of organisations so the Treasury is not today saying something radical or unexpected.

"This comes after Christine Legarde saying a range of outcomes from bad to very, very bad, it comes after the Bank of England governor saying in a succession of interviews giving a very clear opinion that this is the biggest domestic risk for the British economy."

He also denied that the Remain campaign was focusing on the negatives. "Ours is a hugely optimistic case but I make no apologies for spelling out the downside. With a market of 500 million people, if you give that up, it goes without saying we are going to be a poorer country."

In response, the Vote Leave campaign said the worse-case scenario painted by the Treasury was worse than the Great Depression of the 1930s and said the Treasury had been "hopelessly wrong" in previous forecasts, including in its support for the Exchange Rate Mechanism in the early 1990s.

Mr Duncan Smith said he did not believe there would be any "economic shock" from leaving, citing economists who have argued the economy would be able to add nearly a million new jobs by avoiding regulation and negotiating new trade deals.

The former cabinet minister claimed that all economic forecasts "eventually proved to be wrong".

He told BBC Radio 4’s Today programme: "Every Treasury report has a central presumption from which there are downsides and then there are upsides. They have chosen today to only produce the downsides...That makes this report categorically unfair and biased. I don't think that downside exists for the UK."

In a separate development, Mr Duncan Smith accused Business Secretary Sajid Javid of privately backing Brexit, even though he publicly supported the EU Remain campaign.

The Essex MP said was "deeply disappointed" in his former cabinet colleague given that he had “privately said how much he wanted the UK to leave the European Union; he is now defending this terrible report".

Pressed on whether Mr Javid had said to him he wanted out, Mr Duncan Smith replied: "He has."

Asked whether that meant Mr Javid was "lying in public", the former Secretary of State said: "He has written it in an article."

Asked on the programme about his previous Eurosceptic views, Mr Javid said: "At that time no one knew what the final deal would be. Look what has been achieved in this renegotiation. Now that's being put to the British people."

He added: "Since the announcement of the referendum we have far more detail of the impact, such as this report, that is coming out."

Later, the Business Secretary rejected Mr Duncan Smith's claim that he had spoken privately about wanting to leave the EU. A Whitehall source said: "This is simply not true. Sajid has said no such thing in private or in public."