LONDON (Reuters) - A post-Brexit trade deal between Britain and the European Union might take 10 years to finalize and could still fail, the United Kingdom's ambassador to the bloc has told Prime Minister Theresa May's government, the BBC reported on Thursday.


Ivan Rogers, Britain's envoy to the EU, warned ministers that the European consensus was that a deal might not be done until the early to mid-2020s and that national parliaments could ultimately reject it, the BBC said.


May's spokesman said this was not the view of Rogers or the government.


The British leader has said she will invoke Article 50 of the EU's Lisbon Treaty, which begins the up to two-year process for leaving the bloc, by the end of March.


"We have been clear all along that we want this to be as smooth and as swift a process as it can be," May's spokesman told reporters.


"Within the timeframe that Article 50 sets out, we will have secured our exit from the European Union with a deal that allows us to trade with and operate within the European single market."

The British government has said it believes it can negotiate its exit alongside talks on its future relationship with the bloc, but some in the EU have said a post-Brexit trade deal cannot be discussed until Brexit is complete.

EU officials have long said that negotiating a trade deal with the bloc can take years, pointing to the fact that Canada started talks in 2009 for an agreement that has yet to enter force.

But British officials have said they hope to reduce the amount of time to strike a deal, arguing that factors such as British regulations already being in line with EU standards after decades of membership, will speed up the process.

Junior trade minister Mark Garnier told parliament on Thursday that some EU deals had been reached more quickly.

"It is very, very difficult to be able to establish exactly how long any trade deal will take," he said.

(Reporting by Sarah Young and Kylie MacLellan; Editing by Stephen Addison)