Arthur Scargill said it felt "normal" to be back on a picket line as he joined striking railway workers in Sheffield on the second day of widespread action.
The union figurehead, now aged 84, was joined by his grandson – who he described as "more militant than me" – outside Sheffield railway station as thousands of members of the Rail, Maritime and Transport (RMT) union staged a second day of walkouts after talks failed.
The action affects 13 train operators, impacting services across the UK.
Only around one in five trains will run and mainly on main lines during the day, dramatically decreasing footfall at many stations as people work from home if they can.
Scargill, who led the miners' strikes in 1984 and 1985, said the RMT was displaying "courage" in taking action and said he was showing his support because "you never stop fighting".
He was applauded as he encouraged other unions to follow the RMT's lead.
Who is Arthur Scargill?
Born to the son of a miner and Communist Party member in Worsbrough Dale, near Barnsley, in 1938, Scargill became a figurehead for the trade union movement.
He was president of the National Union of Mineworkers (NUM) from 1982 to 2002, and became best known for leading the UK miners' strike in 1984–5.
The action turned into a confrontation with the Conservative government of Margaret Thatcher, in which the miners' union was defeated.
Scargill later became leader of the Socialist Labour Party (SLP), founded by him in 1996.
'Now is the time'
Asked how he felt to be back on a picket line Mr Scargill said: "It feels normal, but don't forget I've been on picket lines before," he said.
"I think they [the strikers] are absolutely right, they have got my total support and I would urge all other unions to join with them.
"If they have any sense now is the time to take strike action in order to justify their right to have decent working conditions, working pay."
Mr Scargill's appearance is his second in Yorkshire this week, after he joined a picket in Wakefield on Tuesday, 21 June.
And it comes after the Labour leader, Sir Keir Starmer, told his party's frontbench MPs not to take part in demonstrations with striking workers.
Mr Scargill said it showed "absolute contempt for the very people who formed the Labour Party".
He said: "I couldn't believe any leader would come out and say we're unable to speak to or join a picket line. Even past leaders like Harold Wilson supported the miners' strike."
And he said he believed further strike action was inevitable.
"This should be the summer of building a trade union movement and getting a socialist movement building in Britain," he said.
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