The trade union movement is in shock after the sudden death of rail union leader Bob Crow, who passed away early this morning aged 52
The general secretary of the Rail, Maritime and Transport (RMT) union is believed to have suffered a heart attack at his home in east London.
The RMT announced the news "with the deepest regret" and said his death would leave a "massive gap":
Tributes poured in from unions, politicians and campaign groups, as well as business and industry leaders.
London Mayor Boris Johnson, who was embroiled in a bitter dispute with Mr Crow over Tube ticket office closures last month, said the union leader had fought "tirelessly" for his members.
Mr Crow was one of the most high-profile, left-wing union leaders of his generation, sparking as much anger from passengers hit by rail and Tube strikes, as praise from his members for winning pay rises.
He was constantly involved in industrial disputes and campaigns and led a walkout by London Underground workers last month in a dispute over ticket office closures.
Manuel Cortes, leader of the TSSA rail union, who stood on picket lines with Mr Crow during last month's Tube strike, said he was "admired by his members and feared by employers, which is exactly how he liked it."
Mr Crow was campaigning for the NO2EU party and planned to stand in May's European elections, arguing that workers in the UK were being hit by EU policies.
The RMT parted company with Labour years ago after disagreements over policies, although the union continued to send its affiliation fee to the party, only to have its cheques returned.
Labour leader Ed Miliband said:
While Deputy Prime Minister and Liberal Democrat leader wrote:
Transport Secretary Patrick McLoughlin said although they "may not always have agreed on how to run our railways", the RMT leader was "a powerful advocate who led his organisation from the front" .
Mr Crow's counterparts from trade unions joined in paying tribute to the firebrand: