Michael Colvin, MP for Romsey and Waterside in Hampshire, succeeded Mr Hamilton as a consultant to Strategy Network International, a public relations firm with strong links to political interests in southern Africa.
The revelation that another MP did not register a financial interest follows yesterday's Independent report that SNI briefly employed Mr Hamilton when he was a backbencher. Mr Hamilton, already under fire over the acceptance of a free hotel stay from Mohamed al-Fayed, owner of Harrods, likewise did not reveal his connection with the firm.
Mr Colvin, 62, who had a long-standing interest in South Africa, took up the appointment in 1991. He said last night: 'It was an oversight that I regret.' Earlier, his wife Nichola said he had only worked for the firm for about six months and that it was 'a sort of trial'.
The latest twist in the affair, which only came to light because Mr Hamilton's links with SNI had been revealed, will fuel concerns about the extent to which rules on registration of members' financial interests have been flouted.
Mr Colvin, like Mr Hamilton, was recommended to SNI by Derek Laud, a prominent figure on the Tory right. Mr Laud is managing director of Ludgate Laud, another political lobbyist. Mr Colvin is a director.
A Lloyds Name, Mr Colvin was among several Conservative MPs who refused to declare details of their syndicates, earning a rebuke from the Commons Select Committee on Members' Interests, which polices registrations.
Michael Howard, the Home Secretary, last night defended his intervention in a citizenship application by the al-Fayed family as John Major prepared to publish the findings of the official inquiry into the parliamentary 'cash for questions' allegations.
Mr Major was considering new steps to defuse the mounting row over the latest succession of scandals. But prominent right-wing Tories rallied to Mr Hamilton's defence.
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