Ex-Tory MP Sarah Wollaston has defected to the Liberal Democrats.
Dr Wollaston, 57, who was elected as a Tory MP in 2010, takes the number of Lib Dems in Parliament to 14 after the party won the Brecon and Radnorshire by-election this month.
The Totnes MP resigned from the Conservatives over the party's handling of Brexit in February and briefly joined defectors party Change UK.
Since the party’s dismal failure in the European elections she has sat as an independent MP.
The Remain supporting MP becomes the second member of that group to join the Lib Dems, following Ex-Labour MP Chuka Umunna.
Dr Wollaston was one of three Conservatives who quit the party in February to join Labour defectors in The Independent Group.
In a post on her website to explain the decision to her constituents, Dr Wollaston said she made the decision because Brexit had "sucked all the political oxygen from the government".
She added: "Just as we could and should have been benefitting from economic recovery after years of austerity, that has been put into reverse because of the march to No Deal"
"Good ideas rarely require planning for mass bailouts of collapsing businesses including farming or the emergency air-freighting of vital medicines and food supplies.
"This is money that could, and should have been spent tackling poverty, improving life chances and genuinely providing new resources for priorities like education, policing, social care and the NHS.
"Britain deserves better, and my fellow MPs need to read the evidence and act in the national interest rather than Party interest, and they need to act now before it is too late."
Leader of the Liberal Democrats, Jo Swinson said: "I am delighted to welcome Sarah to the Liberal Democrats.
"We have worked together for many months to fight to stop Brexit and, as one of the most respected Members of Parliament, she brings real expertise to our team.
"The Liberal Democrats are growing – over 30,000 people, alongside Sarah, have joined us since our best ever results in the European Elections in May. As the strongest party for Remainers, we will lead the fight to stop Brexit."
GP Dr Wollaston is a powerful figure in Parliament where she chairs both the Health and Social Affairs Committee and the Liaison Committee, which quizzes the PM.
