As negotiations for Britain's departure from the EU rumble on, a new pro-EU opposition party led by the government's former Brexit adviser is poised for a September unveiling.

'The Democrats', which pitch themselves as an anti-Brexit, centrist party, unveiled on Twitter Monday its logo and the sale of branded merchandise as it seeks to raise support – and funds – for an event scheduled to take place in London on September 9.

The announcement was made by James Chapman, who previously worked as Brexit Secretary David Davis' chief of staff within the government's Department for Exiting the European Union.

Since quitting the role, Chapman, the former political editor of the Daily Mail, has been vocal in his rejection of the U.K.'s decision to leave the EU and has cited support from several other members of parliament, including the current Conservative government.

The make-up of the prospective party is as yet unclear. When contacted by CNBC via Twitter, Chapman said that further details would be released in September.

TWEET

In a series of Tweets this morning, he did however highlight intentions to focus on increased borrowing for investment in infrastructure, as well as healthcare and pension reforms.

He also called on other leaders, including Democrat Hillary Clinton and leader of the U.K.'s existing pro-EU, center-left Liberal Democrats party, Vince Cable, for support.

TWEET

T-shirts brandishing slogans such as 'Exit from Brexit' and 'Darling they lied…' are available to purchase from the Democrat's affiliated website 'demarcationdesign' from £18.00 ($23) while mugs are available for $12.

"Working with James Chapman, we've designed a logo and a range of tees celebrating the launch of a new party dedicated to stopping Brexit and reclaiming the centre ground of British politics," the website reads.

£1 ($1.20) from each sale will go to Fight Brexit War Chest, a pro-EU crowd funding page providing funding for rallies and conferences. So far the page has raised £35,000 of a £60,000 target.

British citizens are free to establish and register their own political parties. There are currently approximately 500 in the U.K. but just over a dozen with notable backing.

Anthony Wells, director of political and social opinion polling and market research firm YouGov, told CNBC that the success of the party would hinge on the support Chapman can garner from high-level politicians.

"If (Chapman) got some serious figures then it would be taken extremely seriously and would get huge amounts of backing," Wells suggested over the phone.

"It really is about the people and the context," he said.

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