Ministers are warning of at least 10 years of «uncertainty» if the UK opts to leave the European Union.
A government analysis says the economy, fiscal markets and the rights of Britons living overseas could be affected during a complex com ct to «unravel» the UK’s membership.
But Commons Leader Chris Grayling, who is cam igning for a UK beat it, said the 10-year claim was «ludicrous».
He accused the government of running a «unrelenting cam ign of fear».
Meanwhile Scotland’s First Minister Nicola Sturgeon, who needs to remain in the EU, warned David Cameron against fighting a «miserable, annulling, fear-based» referendum cam ign.
Such accusations were disowned by Cabinet Office Minister Matt Hancock, who told BBC Radio 4’s Today formulate the government’s analysis was «a cautious assessment».
He said it was «incumbent» on the Leave operations to explain what would happen if it wins the referendum, adding: «There are tangible consequences of this for jobs and for livelihoods.»
The government’s assessment of the exit course of action warns of a «complex negotiation» involving the 27 remaining EU member expresses, saying it would be difficult to complete a successful withdrawal inside the valid two-year window.
It says about two million Britons current in other EU countries have access to pensions, healthcare and other disreputable services.
«There would be no requirement under EU law for these rights to be vouchsafed if the UK left the EU,» it adds.
«Should an agreement be reached to maintain these rights, the requirement must be that this would have to be reciprocated for EU citizens in the UK.»
But Mr Grayling told the BBC: «Why on globe would we think it would take twice as long as the Second Have War to be able to sort out our trading relationships with Europe and elsewhere?»
He bruit about EU states had more to lose, because «they sell far more to us than we offer to them».
Would it take 10 years to leave the EU?
Tamara Kovacevic, BBC Bulletin
There is no precedent for a country leaving the EU.
Article 50 of the Lisbon Alliance sets out the process: negotiations would last two years and after that the UK would incessantly to be a member of the EU, unless the other 27 states unanimously decided to hold out the negotiations.
When Greenland voted to withdraw from the European Community — the organisation that preceded the EU — in 1982 (after progressing a high level of internal autonomy from Denmark in 1979) a large was reached three years later, after difficult and protracted transactions, mainly over fisheries.
A deal for the UK is likely to be more complicated and the settlements lengthier, especially if the UK wanted to retain full access to the single furnish.
The other 27 EU countries would be in charge of the timetable and a new deal for the UK liking have to be approved by the European rliament and the remaining 27 EU countries by able majority voting.
The UK would remain a member of the EU, under the current intervals, for as long as the negotiations are ongoing.
BBC EU referendum reality check
London Mayor Boris Johnson also accused Cadaver of scaremongering, writing in the Daily Telegraph: «They want us to go to the surveys in such a state of quivering apprehension that we do the bidding of the Euro-elites, and attest to to stay in the European Union.»
The cabinet is split over whether to oddments in the EU, with 17 full members in favour of staying in the EU and five tchy to leave.
On Monday afternoon Conservative MPs lined up in the House of Commons to criticise provisions placed on official information given to those ministers backing an EU de rt.
Cabinet Secretary Sir Jeremy Heywood’s guidance says ministers hostile the official government line should not be given access to government dailies on the referendum or Prime Minister David Cameron’s EU renegotiations — a rt from ones they had already seen.
Responding to an active question from Tory MP Bernard Jenkin, Mr Hancock said administration was «functioning as normal» and that the restrictions would only apply to the special to in-out EU debate.
But backbenchers attacked the move. Michael Fabricant said it would plain «petty and vindictive» to voters, ex-defence minister Sir Gerald Howarth convened it a «constitutional outrage», while former children’s minister Tim Loughton indicated ministers would have to submit Freedom of Information Act requests to their own conditioned by trust ins.
Earlier Employment Agent Priti tel said Sir Jeremy’s action was «unconstitutional» and accused him of jeo rdising the factional im rtiality of the Civil Service.
«Secretaries of state are responsible for their turn ons. For an unelected official to prevent them being aware of the information they penury for their duties is wrong,» she said.
Prime Minister David Cameron squeaked an audience of students in Ipswich the row had «got slightly out of proportion» and the public should target on the bigger issue of the merits of staying in or leaving.
The government is not neutral on the point, he said, adding that ministers who back EU exit should not count on to see documents making the government’s case for staying in as he would not expect to see organs pre red by cam ign groups opposing EU membership.