Any Government would have to introduce an emergency Budget involving tens of billions of pounds of spending cuts and tax rises if Britain votes to leave the EU next week, George Osborne and Alistair Darling will warn.

In a sign that the Remain campaign intends to double down on project fear, the Chancellor and his immediate predecessor will claim that such a budget would be necessary to plug a black hole in the public finances as a result of Brexit.

Mr Darling is expected to add that he is “more worried now” about the consequences of Britain pulling out of the EU than he was at the time of the financial crisis in 2008.

Sharing a joint platform Mr Osborne and Mr Darling will set out £30 billion of illustrative measures that, they say, would need to be taken in an emergency Budget.

This, they claim, is a mid-range estimate, based on the Institute for Fiscal Studies’ assessment of the impact of a vote to leave on the public finances because of lower trade, investment, and tax receipts.

It includes £15 billion in tax rises, comprising a two pence rise in the basic rate of income tax to 22 per cent, a three pence rise in the higher rate to 43 per cent, and a five pence rise in inheritance tax rates to 45p. Alcohol and petrol duties would rise by 5 per cent.

In addition they say that £15 billion in new spending cuts could mean NHS, education and defence spending being slashed by two per cent – meaning a £2.5 billion a year cut to the health service, a £1.2 billion cut to defence and a £1.15 billion cut to education. Pensions spending could be cut by £2 billion a year.

Spending in other areas, including the Home Office and policing, transport and local government, could take a five per cent cut, saving £5.8 billion.

All, they say, take into account any supposed ‘windfall’ from reduced EU budget contributions.

The move suggests that the Remain camp have no intention of scaling back the rhetoric on the financial consequences of a Leave vote – despite public scepticism of the claims.

To pull back now, they believe, would lead to claims from the Leave camp that they never believed the warnings in the first place.

They are also confident that the strategy will ultimately be effective when people come to cast their ballots on 23 June.

Mr Osborne and Mr Darling will also denounce Leave campaign claims that Britain would have more to spend on public services if it leaves the EU as a “con” being attempted on the British people.

“Far from freeing up money to spend on public services as the Leave campaign would like you to believe, quitting the EU would mean less money. Billions less,” Mr Osborne will say.

“It's a lose-lose situation for British families and we shouldn’t risk it.

“If you doubt it, look at what’s happening on financial markets. The economic uncertainty the Leave campaign blithely insists won’t be caused by a vote to leave is already being seen.”

What has the EU ever done for us? Show all 7 1 /7 What has the EU ever done for us? What has the EU ever done for us? 1. It gives you freedom to live, work and retire anywhere in Europe As a member of the EU, UK citizens benefit from freedom of movement across the continent. Considered one of the so-called four pillars of the European Union, this freedom allows all EU citizens to live, work and travel in other member states. What has the EU ever done for us? 2. It sustains millions of jobs A report by the Centre for Economics and Business Research, released in October 2015, suggested 3.1 million British jobs were linked to the UK’s exports to the EU. What has the EU ever done for us? 3. Your holiday is much easier - and safer Freedom to travel is one of the most exercised benefits of EU membership, with Britons having made 31 million visits to the EU in 2014 alone. But a lot of the benefits of being an EU citizen are either taken for granted or go unnoticed. What has the EU ever done for us? 4. It means you're less likely to get ripped off Consumer protection is a key benefit of the EU’s single market, and ensures members of the British public receive equal consumer rights when shopping anywhere in Europe. What has the EU ever done for us? 5. It offers greater protection from terrorists, paedophiles, people traffickers and cyber-crime Another example of a lesser-known advantage of EU membership is the benefit of cross-country coordination and cooperation in the fight against crime. What has the EU ever done for us? 6. Our businesses depend on it According to 71% of all members of the Confederation of British Influence (CBI), and 67 per cent of small and medium-sized enterprises (SMEs), the EU has had an overall positive impact on their business. What has the EU ever done for us? 7. We have greater influence Robin Niblett, Director of think-tank Chatham House, stated in a report published last year: “For a mid-sized country like the UK, which will never again be economically dominant either globally or regionally, and whose diplomatic and military resources are declining in relative terms, being a major player in a strong regional institution can offer a critical lever for international influence.

Mr Darling will add: “I am even more worried now than I was in 2008.

“The Leave campaign has no idea, no plan whatsoever. Any political party seeking election on such a flimsy and fraudulent prospectus would have been torn to pieces by now.

“We know we'll have not just a short period of uncertainty - but years and years of it. Far from having more to spend on public services - the giant con trick at the heart of the Leave campaign - we'd have tens of billions of pounds less. As a former Chancellor, I have to tell you that would mean an emergency Budget where we would have to increase taxes and cut spending.

“Why on earth would we inflict that on ourselves all over again?”