GEORGE Osborne’s claim that leaving the European Union would cost the Treasury £36 billion in lost tax revenue, requiring an 8p income tax rise to fill the financial black hole, has been denounced by the Leave camp as absurd and unbelievable.

The chancellor upped the ante in the EU referendum debate by publishing a 200-page Treasury analysis, which suggested a vote to leave would result in Britain being “permanently poorer”.

In an exercise similar to that used during the Scottish independence referendum campaign, the department posited three potential options of varying degree for the UK if it left the EU: the status currently enjoyed by Norway, which makes payments to the EU and accepts free movement in return for access to the single market; a bilateral free trade deal of the kind obtained by Canada or a relationship under the rules of the World Trade Organisation.

Mr Osborne focused his assessment on the mid-placed Canada-style model, which has previously been championed by leading Brexiteer Boris Johnson, the London mayor.

In this scenario, the UK economy would become 6.2 per cent smaller by 2030, the equivalent of £4,300 per household.

"Under any alternative, we'd trade less, do less business and receive less investment. And the price would be paid by British families. Wages would be lower and prices would be higher," declared the chancellor.

Speaking in Bristol as he launched the Treasury document, he rejected the claims of Leave campaigners that the country would benefit from the savings made by not contributing to Brussels' coffers.

"Don't believe the flimsy claim that at least we would get some money back by not paying our 1p on every £1 we raise in taxes to the European budget. We'd lose tens of billions of pounds in money for our public services because our economy would be smaller and our families poorer.”

Mr Osborne added: "The most likely bill our public services would pay for leaving the EU is £36bn; that's the equivalent of 8p on the basic rate of income tax."

The Treasury document suggested the Norway option would have the least impact, seeing GDP fall by a central estimate of 3.8 per cent, the equivalent of £2,600 per household, losing the Exchequer £20bn a year while the WTO option would have the greatest impact with the respective figures of 7.5 per cent, £5,200 and £45bn.

Frances O'Grady, the TUC general secretary, said the Treasury document was a "sobering reality check" while Unison's Dave Prentis warned Brexit could push public services "over the edge".

But anti-EU campaigners lined up to dismiss Mr Osborne’s claims.

Pro-Brexit Tory MP Andrew Percy complained: "Project Fear turned into Project Utter Crap today," while arch-eurosceptic John Redwood dismissed the Treasury's claim of a £4,300 Brexit cost to families as "absurd".

Lord Lamont, the former Tory chancellor, said: “The chancellor has endorsed a forecast which looks 14 years ahead and predicts a fall in GDP of less than 0.5 per cent a year; well within the margin of error. Few forecasts are right for 14 months, let alone 14 years. Such precision is spurious and entirely unbelievable."

Matthew Elliott from the Vote Leave campaign said the Treasury report's figures were "deeply flawed".

Mr Osborne also faced questions over the document’s assumption that net migration would fall to 185,000 a year from 2021 onwards; still far in excess of the UK Government's goal of reducing it to the "tens of thousands". Leave supporters argued the Treasury had failed to take into account the costs of coping with an ever-growing population.

Nigel Farage, the Ukip leader, tweeted: “Treasury report clear: stay in EU and population will explode, over 3m increase by 2030. EU means mass migration.”

Meantime, the Commons Environmental Audit Committee today said the UK's EU membership had been a "crucial factor" in driving forward polices on air and water pollution and protecting wildlife.

It said its inquiry found the "overwhelming view" of witnesses across the sector was that EU membership had been positive for the UK environment.