A failure by MPs to back disclosure of MPs' earnings from consultancies would damage the honour and reputation of Parliament in the eyes of the electorate, a member of the Nolan Committee on Standards in Public Life said yesterday.
The warning came as more Tory backbenchers joined the growing rebellion against the Government's refusal to go along with the original Nolan recommendation for disclosure.
Approaching two dozen MPs were yesterday prepared either to vote against the Government or abstain, threatening a cliffhanger vote in the House on Monday.
The MPs are, however, currently split into two groups, one arguing for disclosure with immediate effect and the other backing implementation after the next election.
Peter Thurnham, MP for Bolton North East, and Sir Teddy Taylor, MP for Southend East, were yesterday circulating a draft amendment for Monday's debate in the hope of garnering backing for an all-party amendment reflecting the latter position.
Meanwhile, Anthony King, Professor of Politics at Essex University, was the first member of Lord Nolan's committee to speak out after Wednesday's report on implementation of its recommendations by a select committee of MPs.
"The question here is one of the honour and reputation of parliament," Professor King said in an interview with BBC Radio 4's The World at One.
He said the issue had become party political - a view privately shared by some Tory MPs yesterday, who felt John Major has leapt too swiftly to the defence of the Conservative majority on the select committee.
Professor King said: "If the House of Commons does turn down this part of the Nolan committee's recommendations, then I am sure the Labour Party will go on hammering away at the Conservatives and I am sure a lot of voters will be deeply displeased."
He said the select committee had produced a "very impressive report, but the paid advocacy ban would not stop MPs lunching with or chatting to ministers".
Professor King's stance was soon contradicted by another Nolan committee member, Tom King, the former Conservative cabinet minister, at Prime Minister's Questions - although he was the only Tory backbencher to defend non-disclosure as Labour MPs launched an onslaught on Mr Major.
Tony Blair, the Labour leader, challenged the Prime Minister: "Having set up Nolan and having agreed to implement it, what possible justification are you going to give when you come to the House of Commons on Monday, along with the Cabinet and the Government, and vote down its key recommendation?"
The advocacy ban reverses the inroads made by rules on the Register of Members' Interests on the so-called 1947 Resolution, which outlaws MPs selling their services.
But the Conservative-dominated select committee made only a limited attempt to stop MPs circumventing it in Wednesday's report - a provision that any delegations to ministers or officials introduced by an MP with a declarable interest should be recorded in the Register of Members' Interests. Letters and other forms of contact are not mentioned, and the provision merely reflects the old system under which activities were allowed as long as they were registered.
Dale Campbell-Savours, Labour MP for Workington, last night tabled amendments seeking to plug that gap by stopping members with interests lobbying ministers through meetings or correspondence.
Labour claims that many MPs will get round the advocacy ban by getting contracts with outside interests defined as purely advisory, and it argued yesterday that the select committee report had simply banned advocacy under contracts obliging MPs to lobby on behalf of the interests they represented. It did not address the issue tackled by Lord Nolan in his report, where he said: "the  resolution does not prohibit members from voluntarily speaking, lobbying or voting in support of their clients' interest if the members think it right to do so".