Alastair Newton, a former adviser to ex-PM to Tony Blair, authored the 11-page study in which he said the EU may be forced to take drastic steps towards fiscal union to save the euro, making it impossible for a sovereign state like the UK to remain.
A referendum could then be called in the UK, leading to a ‘Brixit’ before the end of the year.
An extract from the report, printed in The Telegraph, said: “A deepening of the eurozone crisis in the immediate future remains a real possibility despite the recent efforts of the ECB in particular to calm markets.
“This, in turn, could spur acceleration in integration in order to try to prevent the collapse of the eurozone, thereby advancing projects which are likely to prove difficult for the British government.
“It is only a matter of time, in our view, before crisis-related steps are agreed which necessitate treaty changes.
“In those circumstances, the British government will almost certainly demand ‘treaty change for treaty change’ in an effort to repatriate powers, i.e. be looking to win repatriation of powers to London for every concession on treaty reform sought by the eurozone on a one-for-one basis.”
Meanwhile, in a separate report by Reuters, Blair told a German newspaper he is “deeply worried” Britain might leave the European Union in a referendum, if too many powers were transferred to Brussels without democratic legitimacy.