Britain's Liberal Democrats on Thursday unveiled "Bollocks to Brexit" as their stark new campaign slogan in the European Parliament election campaign.

The centrist party, which performed well in council elections last week, is seeking to beef up its credentials as the traditional pro-European party.

"We've been the pro-Europe party for 50 years," party leader Vince Cable said in an interview with The Guardian.

The Liberal Democrats are facing competition from Change UK, a new group of former Conservative and Labour MPs who also oppose leaving the EU and want a second referendum on Brexit with an option for Britain to remain in the EU.

The "Bollocks to Brexit" slogan has until now been used only by campaigners, including flamboyant businessman Charlie Mullins who has put up a giant poster with the phrase above the offices of his company Pimlico Plumbers.

The word "bollocks" - used in British English - means both rubbish and testicles and was made world-famous by the Sex Pistols punk album "Never Mind The Bollocks".

The Guardian said "more squeamish" Liberal Democrat candidates would be able to use campaign literature containing the more toned-down slogan "Stop Brexit".

Pro-Brexit campaigner Darren Grimes was not amused, saying that the party was "so desperate for attention that it's willing to stick two fingers to the millions who voted for, and believe in, Brexit".

The main national parties opposing Brexit, the Liberal Democrats, Change UK and the Greens, have failed to form an alliance ahead of the May 23 vote.

The Brexit Party, led by Nigel Farage, is topping the polls with a simple message that the government has betrayed the result of the 2016 Brexit referendum.