Jeremy Corbyn has led well-wishers after it emerged the Second World War veteran and political activist Harry Leslie Smith is seriously ill in hospital.
The 95-year-old was “not in a good way” and had been taken into A&E, his son, John, said.
The Daily Mirror said Mr Smith was understood to have fallen ill in Canada, where he was visiting his son.
Born in Barnsley, South Yorkshire, Mr Smith served with the RAF in Germany and in recent years campaigned on behalf of the NHS.
On Wednesday morning, #IStandWithHarry was trending on Twitter as messages of support flooded in.
Mr Corbyn said: “Very sorry to hear this. Please pass on my best to Harry. We need him to get well soon as the National Health Service, and our movement, needs him.”
Shadow transport minister Karl Turner added: “Very much hope Harry makes a full recovery. We need him.”
A tweet posted on @Harryslaststand on Wednesday morning said: “It is after midnight here but I think he will see the morning and then we will go from there.”