Stephen Timms, who became a Social Security minister in July, has neither sold his shares in Ovum Ltd nor placed them in trust.
Conservatives attacked Mr Timms last night for holding on to the shares. He worked for the firm for eight years before becoming an MP in 1994.
Iain Duncan Smith, Conservative social security spokesman, said: "If Mr Timmsreceived advice that he didn't need to sell these shares or place them in trust, I would question that advice. The social security department uses huge amounts of computer and telephone services."
A spokeswoman for the department said she did not believe Mr Timms had to sell the shares because there was no obvious conflict of interest. "It is a small company. It publishes research reports and does other consultancy work. We wouldn't buy what they have to offer and there is no rule a minister cannot own shares."
Labour MPs were also eager to use the register to score political points. Chris Leslie, Labour member for Shipley, made a formal complaint that the Tory leader, William Hague, had not detailed his privateflights in his entry declaring he often received hospitality andtransport. Several ministers, including the Sports minister, Tony Banks and the Secretary of State for Culture, Chris Smith, made general declarations like Mr Hague's. They were cleared by the registrar.
The register allowed more than one MP to list interests they had previously failed to mention. Peter Mandelson, the former secretary of state for trade, registered his loan from Geoffrey Robinson, the former paymaster general. Edward Heath, the former prime minister, listed five advisory posts that had been the subject of complaints against him.
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Ann Widdecombe, Conservative Health spokesman, registered "one BBC teaspoon, bent and signed by Uri Geller. Intrinsic value nil. Value added according to Geller considerable."
Anthony Steen, Conservative MP for Totnes, registered "crabs and lobsters" given in recognition of his efforts on behalf of the industry.
Fiona Mactaggart, Labour MP for Slough, received a Fortnum and Mason hamper but gave it away to voluntary organisations.
John Major took 10 foreign trips between April and November 1998, including six to the United States.