MI5 briefed bosses on subversives at work

When Edward Heath was Tory Prime Minister, he ordered MI5 secretly to brief senior industrialists about "subversive" organisations trying to infiltrate their workplaces, files released to the National Archives under the 30-year-rule show. Mr Heath, now Sir Edward, intervened after MI5 said disclosing intelligence to industrialists could undermine their operations.

Tim Powell, chairman of tractor-builder Massey-Ferguson, had complained to him that they had no way of knowing if they were recruiting "troublemakers" who could then prove impossible to sack.

Over lunch with Mr Heath's political secretary Douglas (now Lord) Hurd, Mr Powell asked if he could be supplied with "a list of organisations they should watch out for" when recruiting staff.

Initially, the request was blocked by the Cabinet Secretary, Sir John Hunt. "Anything in the nature of an official black list might both hamper the work of the Security Service (MI5) and put the Government of the day at risk of attack for interfering in the employment field (libel, wrongful dismissal, etc)," Sir John warned Mr Hurd.

He suggested that Mr Powell should be referred to "unofficial sources" such as the right-wing Economic League.

But Mr Heath' premiership had been dogged by strikes and industrial unrest. He ordered his private secretary, Robert Armstrong, to write back to Sir John, telling him Mr Powell was "too serious a person to be dismissed with a reference to the Economic League" and suggesting that he should be given "some degree of oral briefing".

Far from objecting, Sir John said he fully shared the Prime Minister's view. "But I was completely unable to get either the Home Office or the Security Service to agree," he wrote to Mr Armstrong. "Encouraged by your letter I am now returning to the charge."

Shortly afterwards, Sir John confirmed that a briefing with a senior official had in fact been arranged.