Liberal Democrats should support the UK rejoining the European Union if Brexit takes place, the party's foreign affairs spokesman Chuka Umunna has said.

His remarks came after the unequivocally pro-EU party officially endorsed a new policy of revoking Article 50 without a referendum if leader Jo Swinson wins power at the next general election.

But if Boris Johnson does succeed in severing Britain's ties with the EU, Mr Umunna made it clear on the fringes of the Lib Dems' annual conference in Bournemouth he would campaign for the UK to rejoin the bloc at a future date.

He also failed to rule out his support for joining the Euro and any "European army" that could be established by the the EU 27 as a condition for the UK reestablishing its membership.

Asked by The Independent's editor, Christian Broughton, whether he would back Britain rejoining the bloc if Brexit happens, he replied: "Yes. But I don't accept that we're going to leave the European Union."

Peterborough by-election: Brexit Party loses out to Labour Show all 14 1 /14 Peterborough by-election: Brexit Party loses out to Labour Peterborough by-election: Brexit Party loses out to Labour Peterborough By Election Independent candidate Bobby Elmo Smith watches the by-election count on June 07, 2019 in Peterborough, England. Brexit Party candidate Mike Greene is looking to become the Brexit Partys first MP to Westminster in the Peterborough by-election, which was triggered following the removal of former Labour MP Fiona Onasanya by a recall petition. Getty Peterborough by-election: Brexit Party loses out to Labour Peterborough By Election 2 Brexit Party leader Nigel Farage in Newborough in Peterborough prior to votes being counted in the Peterborough by-election. PA Peterborough by-election: Brexit Party loses out to Labour Peterborough By Election 3 Lisa Forbes of the Labour Party accepts her win for the local seat after all votes are in and counted at the Kingsgate Conference Centre in Peterborough. AFP/Getty Images Peterborough by-election: Brexit Party loses out to Labour Peterborough By Election 4 Votes are counted at the Kingsgate Conference Centre in Peterborough, England on June 6, 2019. - A local by-election was triggered when Peterborough's former MP Fiona Onasanya was sacked by her constituents in the first successful re-call petition prompting a by-election AFP/Getty Images Peterborough by-election: Brexit Party loses out to Labour Peterborough By Election 5 Votes are counted at the Kingsgate Conference Centre in Peterborough, England on June 6, 2019. - A local by-election was triggered when Peterborough's former MP Fiona Onasanya was sacked by her constituents in the first successful re-call petition prompting a by-election. AFP/Getty Images Peterborough by-election: Brexit Party loses out to Labour Peterborough By Election 6 Votes are counted at the Kingsgate Conference Centre in Peterborough, England on June 6, 2019. - A local by-election was triggered when Peterborough's former MP Fiona Onasanya was sacked by her constituents in the first successful re-call petition prompting a by-election. AFP/Getty Images Peterborough by-election: Brexit Party loses out to Labour Peterborough By Election 7 Lisa Forbes of the Labour Party accepts her win for the local seat after all votes are in and counted at the Kingsgate Conference Centre in Peterborough. AFP/Getty Images Peterborough by-election: Brexit Party loses out to Labour Peterborough By Election 8 Lisa Forbes of the Labour Party accepts her win for the local seat after all votes are in and counted at the Kingsgate Conference Centre in Peterborough. AFP/Getty Images Peterborough by-election: Brexit Party loses out to Labour Peterborough By Election 9 Labour Party faithful cheer as Lisa Forbes accepts her win for the local seat after all votes are in and counted at the Kingsgate Conference Centre in Peterborough. AFP/Getty Images Peterborough by-election: Brexit Party loses out to Labour Peterborough By Election 10 Labour Party faithful cheer as Lisa Forbes accepts her win for the local seat after all votes are in and counted at the Kingsgate Conference Centre in Peterborough. AFP/Getty Images Peterborough by-election: Brexit Party loses out to Labour Peterborough By Election 11 Alan "Howling Laud" Hope of the Official Monster Raving Loony Party (L) and party faithful arrive at the Kingsgate Conference Centre in Peterborough. AFP/Getty Images Peterborough by-election: Brexit Party loses out to Labour Peterborough By Election 12 Alan "Howling Laud" Hope of the Official Monster Raving Loony Party (C) and party faithful arrive at the Kingsgate Conference Centre in Peterborough. AFP/Getty Images Peterborough by-election: Brexit Party loses out to Labour Peterborough By Election 13 Mike Greene (C) of the Brexit Party confers with party members at the Kingsgate Conference Centre in Peterborough, England on June 6, 2019. - A local by-election was triggered when Peterborough's former MP Fiona Onasanya was sacked by her constituents in the first successful re-call petition prompting a by-election. AFP/Getty Images Peterborough by-election: Brexit Party loses out to Labour Peterborough By Election 14 By-election votes are counted at the KingsGate Centre in Peterborough. REUTERS

Pressed on whether he would support such a route if it meant signing up to the Euro and European army, he continued: "Look, I don't think that is something that will be demanded of us, not least because about a third of members of the European Union are not part of the Euro, and I do not see them becoming part of the Euro.

"This idea of a European Army I think is unlikely to come about, in the configuration that is suggested by the red-top tabloid newspapers.

"One of the tragedies of the trajectory we are on of potentially leave the EU is of course the EU has to reform. I always thought that going forward you would have an economic core which would revolve around Germany - the main economic powerhouse in the Eurozone - and then it made sense to have a defence and security core that Britain would lead."

On the party's new position of revoking Article 50 and cancelling Brexit if the Lib Dems win power, Mr Umunna said it was a way of ending the chaos.

Labour party conference is a 'hostile environment', says Chuka Umunna

The policy is designed to distinguish the party's central Brexit message from others at Westminster, and ensure they are the most fervently Remain-supporting party at the next election, which could occur as early as November.

Mr Umunna said he would "flabbergasted" if an election did not take place before Christmas, claiming Mr Johnson was unable to govern with a majority of minus 43.

He continued: "I'd be quite surprised if we had a People's Vote before then. I think it's perfectly legitimate for us to treat a clear mandate given to a Liberal Democrat government as authority to revoke Article 50. I think that is absolutely justified.

"Can you imagine if we go to say to poor Brenda from Bristol after that general election, we're going to send you back to the ballot box again. I think in those circumstances it would be completely legitimate."

The ex-Labour MP, who joined the Liberal Democrats in June, also praised the reception he received at this year's annual conference, as he described it as a "homecoming".