Mary Turner, the long standing president of the GMB union and Labour Party executive member has died.
The former dinner lady from London had been ill for years but continued in her post as president, chairing the GMB's annual conference in Plymouth last month.
Labour leader Jeremy Corbyn led the tributes.
He said: "I'm sad to hear of the death of my friend Mary Turner. Mary was such a great campaigner for people. We first worked together in the early 1980s defending school meals in Barnet and I last saw her at a Labour national executive meeting."
He added: "She paved the way for so many women in the union movement and encouraged others to speak out. I send my condolences to Mary's family and her extended family at the GMB union. RIP Mary."
Ms Turner was awarded a CBE for her lengthy political service. This was particularly for her work in the trade union movement, and recognised her lifetime's work for trade union members throughout the UK.
She was elected GMB national president in 1997, was a union activist in the London borough of Brent for many years and represented the GMB on the National Executive Committee of the Labour Party.
Former GMB general secretary Paul Kenny described her as one of the most outstanding trade unionists of her generation.
Mr Kenny said: "Mary never lost her roots. She was hard working and treated everyone the same - from prime ministers to cleaners.
"She was a powerful figure in the Labour Party as well as the trade union movement."
Shadow Home Secretary Diane Abbott paid tribute to Ms Turner on Twitter, saying: “So sad to hear that Mary Turner has passed away. Dinner lady, superstar and titan of the Labour movement #GMB.”
Tim Roache, the current general secretary of the GMB said: “Our great movement lost an incredible person and leader tonight with the passing of Mary Turner. A true fighter and inspiration to all.”
Former Labour leader Ed Miliband also praised Ms Turner’s work. On Twitter he said: “Mary Turner was an extraordinary battler for social justice, equality and working people. Labour has lost one of a kind and one of our best.”
Press Association contributed to this report
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