The European Parliament president said on Wednesday any reversal of Britain's decision to exit the European Union would also need the full backing of the other EU states.

Reversing the process of Brexit was possible, but the rules were very clear, Antonio Tajani told a news conference.

"If Britain decided to change its position, it cannot do it alone. All member states need to decide whether it is possible," he said.

Meanwhile, a leaked EU draft position paper, seen by Reuters, said that the UK will be able to revoke Article 50 before it expires.

The draft also said there should be transitional arrangements to smooth the divorce but no more than three years.

London-based EU agencies, the European Banking Authority and the European Medicines Agency, must move as soon as practicably possible must move, the draft paper said.

The draft sets the red lines for the elected European Parliament on the conduct of divorce talks with Britain before a trade deal can be discussed.

The recognition by the lawmakers that Article 50 can be revoked was seen as a concession to strengthen the hand of Britons who never wanted to quit, despite opposition from the EU chief negotiator Michel Barnier to making references to the reversibility of the process.

But the document, which needs the approval of the whole legislature next week, made it clear that in case Britons changed their mind they would not get a better deal than what they had so far in their relations with the EU.

The Parliament will have a final say on any deal struck with Britain.

The legislature's Brexit team, led by former Belgian Prime Minister Guy Verhofstadt, accepted that in case of Brexit there should be transitional arrangements to smooth the divorce, but stressed they cannot last more than three years and should also be "strictly limited" in their scope.

Negotiations on such transitional arrangements can start only after "substantial progress" is made on a withdrawal agreement that should include a Brexit bill, guarantees for citizens' rights and legal certainties for companies, the document said.

Britain should also recognise that the European Court of Justice, the EU's top court, will be the "competent authority for the interpretation and enforcement of the withdrawal agreement", a statement that may not go down well in London, where many want a quick end of the ECJ powers over Britain.

The Brexit bill should include outstanding commitments to the EU budget and also "provision for off-balance sheet items, contingent liabilities and other financial costs that arise directly as a result of its withdrawal," the document said, raising the prospect of a tab even higher than the 60 billion euros ($64.5 billion) figure circulated in past week