Billericay Tory MP Teresa Gorman has been forced to apologise to MPs after failing to declare her own company on the list of members' interests.
The MP told the House of Commons the omission was an "oversight" after she was forced to apologise to colleagues by the Commons Committee on Standards and Privileges.
The investigation was launched by the Parliamentary watchdog following a complaint from a member of the public.
It rebuked the outspoken MP for failing to register her directorship and shareholding in Banta Ltd.
She was also criticised for not declaring her directorship and shareholding in management consultants Reamfield Ltd.
Mrs Gorman set up Banta Ltd - Biological And Teaching Aids - with her husband James in the 1970s and registered it as a limited company in 1989.
The Tunbridge Wells-based firm makes scientific teaching aids for schools and had a turnover of £150,000 in 1991 before it was bought out in 1997.
Mrs Gorman told the House of Commons she had had "no excuses" for not declaring her interests.
She said: "The Committee on Standards and Privileges has investigated a complaint against me and found that my entry in the registrar of interests was inadequate and incomplete.
"I fully accept the way in which the complaint was investigated and the committee's conclusions.
"The omissions in my entry were due to an oversight on my part. I make no excuses and offer my sincere apologies to the House."
The committee found Mrs Gorman had made a false declaration by failing to declare her directorship of Banta between 1991 and 1993, and had failed to admit being a shareholder between 1989 and 1996.
She was also criticised for not declaring that one of her homes in Norwood in London was used as a business premises.
The original complaint is believed to have come from David Thomas, a fireman from Chesterfield, Derbyshire, who was offended by Mrs Gorman's attack on firefighters.
Apology - Teresa Gorman
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