Anatomy of a plot: Alan Clark, Ian Gow, Richard Ryder and Jonathan Aitken are dining at Green's restaurant in Westminster; Clark describes the scene in his recently published 'Diaries' . . .

A HIGH-LEVEL Conservative conspiracy was hatched to wreak revenge on Michael Mates because of his close association with Michael Heseltine's campaign to challenge Margaret Thatcher for the party leadership.

Supporting evidence of the Tory dirty tricks campaign, recounted in the diaries of the former minister Alan Clark, was provided by Tam Dalyell, the Labour MP, last night.

He told the Independent that in 1990 he had been encouraged by Jonathan Aitken - now Minister of State for Defence - to ask embarrassing Commons questions about Mr Mates's work for a Ministry of Defence

contractor.

Mr Mates, then backbench chairman of the Commons Select Committee on Defence, was forced to drop a consultancy with SGL (Defence) Ltd in May 1990. Three months later he was rebuked in a Commons report for asking questions about flight simulators without mentioning he was a consultant to Link-Miles Ltd, which supplies simulators to the MoD.

The origins of the 'Get Mates' plot are described in the extract published above. Mr Clark was Minister of State for Defence Procurement at the time. His fellow-diners were Ian Gow, the now deceased parliamentary aide to Mrs Thatcher, now Baroness Thatcher; Richard Ryder, then a Treasury minister and the current Chief Whip; and Mr Aitken, a backbench MP.

Mr Clark summed up the grim atmosphere with a reference to Hugh Trevor-Roper's The Last Days of Hitler, and said Mr Aitken had been deputed to 'prime' Mr Dalyell with information designed to destabilise Mr Heseltine's campaign manager.

Mr Dalyell said last night that while he had drafted his own questions, Mr Aitken had provided background information. 'It was natural enough that these people should talk to me. They did, and this prompted my questions,' he said.

One of Mr Dalyell's questions prompted a protest from Mr Mates to the Commons Speaker on 15 May 1990, when he said an allegation made by the Labour MP had been 'specific and wild'.

Demanding an apology, Mr Mates added: 'Had there been the remotest scintilla of truth in it, it would have been shameful if I had been behaving in the way that (he) alleges.'