The leaked letter contained a complaint about the 'injustice' being suffered by Mr Nadir. More importantly, the leak of such a confidential communication suggested further evidence of a dirty tricks campaign against the minister - with further damaging revelations to come.
Mr Mates will face the Commons tonight, when he is scheduled to open a debate on a Northern Ireland security motion.
While No 10 and Sir Marcus Fox, chairman of the 1922 Committee, showed belated signs of a fightback in defence of Mr Mates earlier in the day, the minister's position will be further eroded by continuing revelations from the Tory tabloids.
In his letter to the Attorney General, dated last 17 March, Mr Mates cast doubt on advice given to him by Sir Patrick Mayhew, when he was Attorney General, in October 1991. Sir Patrick - now Mr Mates's Secretary of State at the Northern Ireland Office - had said that the Government did not recognise the Turkish Republic of Northern Cyprus. For that reason, no 'formal approaches' had been made to investigate Mr Nadir's affairs on the island.
Mr Mates then referred to a letter he had received from Sir Nicholas last February, in which he said repeated efforts had been made to 'undertake such a visit . . . but without success'. However, Mr Mates provided the Attorney General with a photocopied document in which a northern Cypriot police commissioner said a Scotland Yard officer and an officer attached to the Serious Fraud Office had visited the island to pursue inquiries into Mr Nadir. The minister also promised to write further 'with evidence about the involvement' in the Nadir case of an Inland Revenue special investigation unit.
Mr Major, meanwhile, is ready to give his support to Mr Mates in a concerted attempt by the Government to weather the continuing storm over Conservative Party funding.
Sir Norman Fowler, the Conservative Party chairman, also upped the ante by calling on John Smith, the Labour leader, to 'disown' Clive Soley, the Hammersmith MP who read out a letter in the Commons chamber on Tuesday night claiming to link Michael Heseltine, President of the Board of Trade, with allegations that Saudi Arabia contributed millions of pounds to the party.