P worked in a closed shop industry. He resigned from his union due to a disagreement and the union threatened to strike unless he was sacked, which he was. He sued the union for damages, which the HL granted, on the grounds of ‘tortious intimidation’ (an ancient tort not used since 1793).
Lord Reid: It was unlawful intimidation “to use a threat to break their contracts with their employer as a weapon to make him do something which he was legally entitled to do but which they knew would cause loss to the plaintiff.” However to find a tort of intimidation there has to be a threat of unlawful action (here the strike would have been unlawful as the collective agreement, incorporated into each of the employee’s employment agreements, prohibited industrial action). While D does what he is legally entitled to do then he is on safe ground.