Lady Lestor, who was 66, had a long and distinguished career during which she also adopted six children as a single mother. She joined the Labour party 40 years ago, went on to become a councillor and was elected MP for Eton and Slough in 1966.
She served in Harold Wilson's and James Callaghan's governments, finally lost her seat in 1983, but returned as MP for Eccles at the following election in 1987.
The Prime Minister paid a warm tribute as soon as he heard the news yesterday. Tony Blair said: "I am deeply saddened to hear of Joan's death. She was a devoted servant of her former constituents, of her party and of her country.
"She was a politician of deep-seated convictions who fought tirelessly for justice at home and abroad."