By Paul Taylor and Noah Barkin
BRUSSELS (Reuters) - The European Union would insist on completing a swift divorce with Britain before starting to forge any new relationship if UK voters decide in June to leave the 28-member bloc.
Two EU sources familiar with the bloc's latest thinking on a possible Brexit told Reuters on Thursday there was no appetite to grant any extension of the two years provided by the EU's Lisbon Treaty for negotiating a withdrawal, while any new trade partnership would take many more years to conclude.
The stark view from Brussels means Britain could initially be cut adrift without any preferential relationship with its biggest trade partner. It contrasts with suggestions by "Leave" campaigners that London could secure a special status preserving market access before it formally leaves the EU.
Top EU officials say they are still confident that Britons will ultimately vote in a June 23 referendum to stay in the community they joined in 1973, despite opinion polls showing a close race.
However in case of a "Leave" vote, the European Commission has tentative plans to hold a rare Sunday meeting on June 26 to set its strategy, one source told Reuters.
EU leaders would hold a brief summit with Britain two days later, at which London would be expected to give formal notice to quit. The 27 other states would then meet without British representatives to decide how to conduct the withdrawal negotiations and take the union forward, based on proposals from the executive Commission.
"It is in our interest to do the divorce as quickly as possible. There's no appetite for negotiating new terms in the first two years," one source said.
Another source said: "The shorter the better. No one wants to go beyond the two years. The show must go on."
Both sources spoke on condition of anonymity because of the acute political sensitivity of any contingency planning for a British departure.
The first source said the initial two-year negotiations would cover only issues such as residual EU budget payments to and from Britain, the pensions of British EU civil servants and relocation of EU agencies based in the UK.
The EU treaty says exit talks can be extended by unanimous vote among all the member states, but both sources said London's partners would want a speedy separation.
Britain would probably leave on July 1, 2018, and become a "third country" in EU parlance. Formal negotiations on some form of trade and partnership agreement could begin only then, the first source said.
In London, Richard Tice, a co-founder of the Leave.eu campaign, said the likely roadmap sketched by EU sources was "Exactly the sort of scaremongering that we have expected from the Remain camp.
"(It) reminds us of the threats people made if we did not join the euro. Brussels has a track record of bullying and denying democracy, but they underestimate the fighting spirit of the British people," Tice said.
Leave.eu, backed by the anti-immigration UK Independence Party, is not the officially recognized "out" campaign, which is called Vote Leave. Vote Leave had no immediate comment.
In case of a vote to remain, the Commission has kept in place a small UK Task Force which helped to craft a deal negotiated by Prime Minister David Cameron in February to meet British concerns on migrant workers' welfare rights and relations with the euro single currency zone.
The seven-member team led by British EU official Jonathan Faull would oversee smooth implementation of the agreement.
That deal lapses automatically if Britain votes to leave, and the first source said a completely different team would be appointed, probably led by a German or French official, to handle exit negotiations.
German and French politicians have warned that London would get no special favors and should expect tough talks in case of a Brexit. EU partners would want to discourage other members from trying to renegotiate membership terms or withdraw.
"Out means out!" Volker Kauder, leader of German Chancellor Angela Merkel's conservative group in parliament said this week.
British Europe minister David Lidington, who supports the "Remain" camp, said on Thursday it was doubtful whether Britain would get any trade agreement with the EU within 10 years.
However, "Leave" supporters have argued that the EU would have to conclude a quick free trade deal with London since the continent has a big trade surplus with the UK and stood to lose exports if tariff barriers were introduced.
(Additional reporting by Alastair Macdonald Editing by Jeremy Gaunt and Andrew Heavens)