The announcement came yesterday evening in a statement posted on the Lib Dems' website - together with the news that she would become the prospective parliamentary candidate for the party in South Cambs. Mrs Allen resigned from the Conservatives earlier this year - over Brexit and other issues with the party - and joined Change UK - The Independent Group, becoming interim leader. She left Change UK in June, and stood as an Independent MP throughout the summer. In a statement, Mrs Allen said: "When I became an MP in 2015, I could never have imagined we would find ourselves in this position. "Through the prudent and practical decisions taken during the coalition years, the economy was recovering and our country was on the up. Coming from business, joining the Conservative Party seemed the logical thing to do. But two general elections and an EU referendum later, the landscape has shifted beyond all recognition. "In February 2019, I resigned from the Conservatives to sit as an Independent MP, because I recognised the party had drifted irreversibly to the right and was more concerned with its own survival than the national interest. "The party had become utterly unrecognisable, uncompassionate and willing to wreck the economy and peace in Ireland by not just contemplating, but actively courting a no-deal Brexit. "The European Elections in May 2019 highlighted the need for MPs to work together in the national interest, putting aside party interests. Voters were crying out for a 'remain alliance' to offer an alternative to the future portrayed by Boris Johnson and Nigel Farage. "Believing that if you get the right people around a table anything is possible, I have always been comfortable with cross-party working. So through the summer and into the autumn, as an independent broker, I have worked with the Liberal Democrats, Green Party, Plaid Cymru and the Independents to build that remain alliance across England and Wales through the organisation I formed - Unite to Remain. "Confident that good progress has now been made on building that remain alliance, I recognise that as with most things in life, I am stronger and more effective when I am part of a team. "Beyond a shadow of a doubt, I know that the best way to serve my constituents and country is to join the Liberal Democrats. "Now is the time to stand shoulder to shoulder with, not just alongside, those I have collaborated and found shared values with. "Shifting to the extremes, the Conservatives and Labour have turned their backs on the liberal, progressive centre ground our country is crying out for. "As we face the monumental task ahead of stopping a damaging Brexit, healing the rifts in society and rebuilding the UK, there is only one party with the honesty, energy and vision to do that - and that is the Liberal Democrats under the leadership of Jo Swinson. "My constituency is liberal and inclusive, bursting with innovation - I am so proud to represent it as its Member of Parliament. I have been bowled over by the support I have received from every corner of it. "My constituents know we are stronger in Europe and they demand better for their country. They know that, although there is a terrifying amount of work ahead of us, together we can build a fairer and more compassionate future for everyone. "I got into politics to make a difference by challenging the status quo. So please help me, support me and join me in the Liberal Democrats - let's do this." Ian Sollom, who had been the Lib Dem PPC for South Cambs until Mrs Allen's defection, tweeted last night to say: "Politics in a liberal democracy is about shaping and making the arguments that win people over to your cause. "So, while I can't pretend I'm not hugely personally disappointed to no longer be standing in South Cambs, I'm genuinely delighted to welcome Heidi Allen to our cause!" Lib Dem Leader Jo Swinson said: "I'm delighted to welcome Heidi to the party. She has been a tireless campaigner for a people's vote and has time and time again put the country's interests ahead of her own. "I'm absolutely thrilled for Heidi to join our fantastic and ever-growing team and I know that her skills, experience and passion will be a real asset to our party. "Heidi is one of 50,000 people who have joined our party as members this year - along with more than 21,000 registered supporters. "Heidi will be standing in South Cambridgeshire as the Liberal Democrat candidate at the next election, and is the seventh MP to join the party in 2019. "In joining the Liberal Democrats, she has called on others to reject the status quo, and unite behind the party's campaign to Stop Brexit. "She has long been an ally in the fight to stop Brexit, and having worked with her I know the energy and passion she will bring to our party. "This once again proves that the Liberal Democrats are the strongest party of Remain. The best deal we have is as members of the European Union, and I look forward to working with Heidi in order to stop Brexit."