But diners at the club were shocked to note his companion: Christopher Morgan, the public relations consultant representing Asil Nadir, the fugitive tycoon. It was Morgan's firm, Morgan Rogerson, who had introduced Mr Mates to the Turkish Cypriot; it was Morgan Rogerson which had encouraged him to raise Nadir's case with the Attorney General; it was Morgan Rogerson from whom he borrowed a second-hand Volvo car which proved to be his undoing.
Mr Mates first met Mr Morgan during the Westland affair in 1986, when Mr Morgan was representing the European consortium bidding to buy the helicopter manufacturer. Mr Mates had an interest because Michael Heseltine was a staunch supporter of the bid and later resigned from the Cabinet when the company was lost to the Americans. Mr Mates had been parliamentary private secretary to Mr Heseltine and ran his unsuccessful campaign for the Tory leadership.
Mr Morgan started to represent Nadir in 1991 - after the founder of Polly Peck had been charged with theft and false accounting involving at least pounds 30m.
But it was not Morgan who first introduced the case to Mr Mates. It was his partner Mark Rogerson, a constituent and friend.
Mr Mates became convinced that Nadir was being pursued unfairly and wrote to the Sir Nicholas Lyell, the Attorney General, to raise his concerns. Mr Mates wrote first in 1991 and, as the Independent disclosed earlier this week, well-placed sources were surprised to discover that the letter bore a close textual resemblance to a draft drawn up for Nadir.
Yesterday, the text of another letter was leaked. 'My concern about the injustice of the way this case is being handled continues to grow,' Mr Mates wrote to Sir Nicholas.
The letter - which Scotland Yard said last night was based on misinformation - was dated 17 March 1993, six weeks before Nadir jumped his pounds 3.5m bail and fled to northern Cyprus. This was before Mr Mates sent Nadir a watch inscribed 'Don't let the buggers get you down]'
He sent the watch after Nadir's trustees-in-bankruptcy had raided his London home and taken his Swiss watch off his wrist as an asset that could be realised to meet some of his debts. Mr Mates felt this was a childish and unnecessary humiliation.
But it was this disclosure that set in train the events that finally made his ministerial position untenable. At first, Mr Mates rode the storm efficiently. He stayed silent.
John Major told the Commons after the watch affair that Mr Mates had made a misjudgement, but it was not a hanging offence. He added: 'I am assured by Mr Mates that he has had no financial involvement with Mr Nadir, nor with any of his companies or with his advisers, either before he became a minister or since.'
Early in the week, there were backbench calls for Mr Mates to resign. Mr Major continued to say Mr Mates had his support. But the endorsement was weaker than it might have been. Mr Major may have been angry because Mr Mates had not told him about the car. Mr Mates kept it secret until, after a challenge from the Independent, he issued a statement. He did so after consulting Downing Street - and Christopher Morgan.
Leading article, page 21