The Liberal Democrats plan to work with the breakaway Independent Group MPs, Oxford West and Abingdon MP Layla Moran confirmed on Wednesday.
The eight Labour splitters were joined by Conservative defectors Anna Soubry, Heidi Allen and Sarah Wollaston, who blamed Theresa May’s Brexit strategy for their resignations.
Speaking to talkRADIO’s Matthew Wright, Ms Moran said she believed the group would bolster opposition to Brexit.
Ms Moran said: “Brexit is a thing that in the immediate term we will absolutely be working together on.
“The stance we’ve taken is that we welcome this, the centre ground is huge and the more people that want to vote for centre ground parties the better.
“Politics ends up going where the momentum lies and if you look at where the people who have left their parties are, they’re proponents for the People’s Vote, they think Brexit is a bad idea and they’re making a case for that.
“Those people listening who agree with that stance should take this as a positive step towards us being more organised in working together to get that delivered.”
While some have compared the Independent Group to the SDP, which split from the Labour Party in 1981, Ms Moran said the new movement was “actually pretty radical”.
“What happened last time there were eventually people who came over from the Conservatives but the original start of it was all Labour, this is more interesting because it’s people from both parties coming together,” she added.