Labour's deputy leader, John Prescott, sent papers on Mr Nicholls's links with World Water Supplies Ltd to Sir Gordon Downey, the Parliamentary Commissioner for Standards, after a Sunday Mirror investigation revealed what it called "a sleazy, secret deal" that could have made the MP for Teignbridge "a multi-millionaire".
Mr Nicholls, a former environment minister and vice-chairman of the Conservative Party, put down 26 Commons questions relating to WWS's work as a manufacturer of water-purifying systems. He also offered to bring the West Country firm into contact with ministers, and actually wrote to Michael Heseltine when he was President of the Board of Trade asking what grants might be available to the firm.
He said in a letter to a WWS director, Richard Whittington, on 8 April, after tabling the Commons questions: "All things being equal, it would be entirely logical that I should become a director and receive a five per cent shareholding."
However, he settled for a position as corporate-affairs adviser, which he declared in the register of MPs' interests. He told the Sunday Mirror that he had resigned the post last Thursday.
Winding-up proceedings against the firm began in Plymouth County Court last week, but two WWS directors will this week fight to keep the company going. They plan to call the MP to give evidence.
Mr Nicholls, whose ministerial career ended abruptly when he was found guilty of drink-driving in 1990, insisted last night: "Had the company been profitable I would have benefited financially and I would have declared that paid interest as I previously registered my unpaid interest. As it is, I received no payment whatsoever from this company."
Labour seized on the case, which emerged only days after Parliament voted to compel MPs to disclose earnings arising from Westminster-linked consultancies. Mr Prescott said the letters written by Mr Nicholls were "a testimony to Tory greed and Tory sleaze"."He may think it is all right for MPs to use their status to get share options, but the majority of MPs do not, and nor do their constituents. MPs of all parties will be appalled."