Shirley Williams, Baroness Williams of Crosby, has died aged 90

Shirley Williams died peacefully in her sleep in the early hours of this morning, the Liberal Democrats have announced on behalf of her family.

Baroness Williams of Crosby, who was aged 90, was best known as one of the “Gang of Four” former Labour Cabinet ministers who split off and founded the breakaway Social Democratic Party (SDP).

Her political career - in the Labour Party, SDP and then the Liberal Democrats - spanned six decades and was marked by passionate support for the European Union.

Ed Davey, Lib Dem leader, said the news of her death was “heartbreaking” personally as well as for the wider party and that he would “miss her terribly”.

“Shirley has been an inspiration to millions, a Liberal lion and a true trailblazer,” he said. “I feel privileged to have known her, listened to her and worked with her.”

Paying tribute to her intellectual, wisdom and generosity, he added: “Shirley had a limitless empathy only too rare in politics today; she connected with people, cared about their lives and saw politics as a crucial tool to change lives for the better.”

He told how her example had inspired him as a young Liberal and said her “vision and bravery, not least in founding the SDP, continues to inspire Liberal Democrats today”.

Lord Newby hailed Baroness Williams as a “charismatic, committed and fearless politician” who believed passionately in a fairer society and in Britain’s membership of the European Union.

“She was an inspiration and mentor to many younger politicians and maintained her campaigning zeal to the end,” he said. “She was central to the formation of the SDP and the Liberal Democrats, and will be greatly missed by many in her extended political family.”

Sir Lindsay Hoyle, Speaker of the House of Commons, remarked that she “enjoyed politics massively – it meant the most enormous amount to her” and added: “If she felt she could do some good in the world, she was happy.

He continued: “She loved elections - and continued campaigning long after she ceased to be an MP - liking nothing better than engaging in debate with people and politicians.

“She was a trailblazer for women and education, one of the first women to sit in Cabinet and the only female member of the ‘Gang of Four’. Without doubt, she was one of a kind, and a character we all shall miss.”

Tributes flocked in from across the opposition benches. Labour's shadow justice secretary David Lammy tweeted: “Very sad Shirley Williams has died. I was lucky to be taught by her at Harvard and to forge a friendship across the political divide in politics.

“Kind, eclectic with the sharpest of minds she was a female pioneer and a giant of the political centre ground.”

Alongside being remembered for her high-profile defection from Labour in the 1980s, her legacy will be defined by her status as a major political thinker.

Former Labour prime minister Tony Blair today declared her “one of the greatest social democrats of the last century, an immense figure of progressive politics through the decades, consistent in her commitment to equality, to social justice, to liberal social democratic values and to internationalism.”

He added: “For many of us in the Labour Party and even after she left it, she remained a source of inspiration and someone to look up to and admire - warm, generous, humane, and uplifting. She will be greatly missed.”

In 2014 Vince Cable, then a Lib Dem MP, said there was “probably no one alive who has done more than her to define and shape British social democracy”.