The RAF veteran survived the Great Depression and Second World War (Picture: Harry Leslie Smith/Twitter).
Second World War veteran and political commentator Harry Leslie Smith has died aged 95.
Mr Smith, from Barnsley in South Yorkshire, championed human rights and the welfare state, and appeared at the Labour Party conference in 2014 to speak about life before the NHS.
A post on his Twitter account, which has more than 250,000 followers, announced his death on Wednesday morning.
The tweet said: "At 3:39 this morning, my dad Harry Leslie Smith died. I am an orphan. #istandwithharry".
The verified Twitter account links to a Facebook page called Harry's Last Stand.
A post on that page, dated 20 November, says: "This is Harry Leslie Smith's son, John. Harry is in A & E and not in a good way. He asked me to inform you in case things don't work out. I will keep you posted."
According to his son John, the 95-year-old was in a critical condition on Wednesday and was suspected to be suffering from pneumonia following a fall.
Former Labour leader Ed Miliband tweeted: "Very sad to hear of the death of Harry Leslie Smith. He was one of a kind who never wavered in his fight for equality and justice. We should all carry his passion, optimism and spirit forward."
Labour MP Jonathan Ashworth wrote on Twitter: "RIP Harry Leslie Smith will always remember this wonderful speech on the NHS you gave at Labour Conference."
Labour MP Luke Pollard also paid tribute, tweeting: "RIP @Harryslaststand. Harry Leslie Smith came to #plymouth ahead of the 2015 General Election. He was old and frail but full of life. His encouragement and positivity was a true inspiration. RIP Harry"
Mr Smith was a pilot during the Second World War and has been a notable campaigner against austerity, gaining a big following on social media and even starting his own podcast.
He rose to prominence in 2013 after writing an article for the Guardian declaring that he would no longer wear a poppy.