Labour peer Lord Alan Haworth has died aged 75, the party has confirmed.
He was a secretary of the parliamentary Labour Party from 1992 to 2004, then became a member of the House of Lords.
The party said he died on Monday morning on holiday in Iceland with wife Maggie Rae.
The pair had been on a cruise of Greenland and Iceland when Lord Haworth fell ill last week. He was helicoptered to hospital in the capital Reykjavik and was treated for bacterial pneumonia.
He died of a heart attack on Monday morning.
Ms Rae praised the doctors and nurses who treated her husband.
“I am obviously heartbroken but I cannot speak highly enough of the Icelandic health service and the doctors and nurses who looked after him,” she said.
“I will never be able to thank them properly for their kindness and their professionalism.”
Labour leader Sir Keir Starmer led tributes to the Blackburn-born peer, who had a keen interest in the party’s history, co-authoring a book on the first 29 Labour MPs elected in 1906.
“Alan Haworth was a dedicated servant of the Labour Party and a diligent student of its history,” said Sir Keir.
“Alan worked for the party in both the House of Commons as PLP secretary and then in the House of Lords as a working peer, without fuss or fanfare but with an absolute determination to make life better for working people.
“He played a key role in delivering Labour’s 1997 landslide and ensuring the party was re-elected. Alan will be greatly missed on both the green and red benches in Parliament.
“My thoughts are with Maggie and all his family and friends at this terrible time.”
Labour’s leader in the House of Lords, Baroness Angela Smith, said: “Alan was Labour to his core with an entertaining, warm-hearted and encyclopaedic knowledge of parliamentary colleagues past and present.
“He was great company and held the respect and affection of all in the Labour Peers Group.
“I am shocked at this news and will miss him dearly.”
Former Labour prime minister Sir Tony Blair said: “Alan was one of my close friends, a wonderful, warm and witty companion.
“You never had a dull evening with Alan, and I had many of them. And there was no one whose counsel I found wiser or more perceptive. He and Maggie were fantastic hosts, generous and loving friends.
“Of course Alan was a huge Labour Party stalwart. But the kind that was no nonsense, let’s get elected so we can do instead of talk.
“And in all the years I knew Alan, he never wavered in his belief in, and commitment to, the party. He served it with distinction and true and dedicated loyalty.
“So I will miss him very deeply indeed. On many different levels. In many different ways. It is a sad day for me, Cherie and all our family.”
There will be a private funeral with a memorial celebration planned for a future date.