James Callaghan called for Arthur Scargill to be “warned off” after he led mass pickets during the notorious Grunwick industrial dispute.

The Prime Minister was so concerned about the long-running and violent dispute that he gave warning that it could become fatal, and even bring down the Government.

Official papers made public today suggest that Mr Scargill, the Yorkshire miners’ leader, and fellow union organ-iser Jack Dromey – now Labour Party Treasurer and husband of Harriet Harman – may have been monitored by MI5.

The Grunwick dispute broke out in the summer of 1976 after the North London film-processing company sacked workers who had joined the Apex trade union, which the company’s owner, George Ward, refused to recognise. By the next summer there were mass pickets as trade unionists from around Britain – including those led by Mr Scargill – arrived in support of Grunwick staff.

Violent clashes with police broke out, and on June 26, 1977, Callaghan told ministers at Chequers that they were “not dealing with respectable unionism but rent-a-mob”.

He added: “If things continue on the present basis there could well be fatalities and in circumstances which might be in danger of bringing the Government down.”

On July 5 he instructed officials: “Keep me informed about Scargill’s movements. He may have to be warned off.”

Ten days later, an official called Graham Angel, based at the Home Office, informed 10 Downing Street that Mr Scargill would reject calls from the TUC to halt the mass pickets.

“Our sources are well aware of Mr Scargill’s wish to resist TUC pressure that mass picketing be ended,” he reported. “Our sources indicate that Mr Scargill has not indicated any definite date for his next action. Mr Dromey of the strike committee has expressed the view that the committee is not ready for another two to three weeks to call for further mass picketing action.”

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