Sir Gordon said in a report that Stephen Dorrell, the Tory spokesman on education and employment, broke a Commons rule by initiating a debate on trade union recognition last month - because he is a director of a clothing firm that does not recognise trade unions.
He said Mr Dorrell's action was a breach of the post-Nolan advocacy rule, barring MPs from initiating a debate or question with a specific and direct impact on their private interests.
The all-party Committee on Standards and Privileges took the rare step of disagreeing with Sir Gordon, and cleared the former secretary of state for health of any misconduct.
But it then added a ruling that will shock the Tory benches, where so many outside business interests are concentrated.
"A case which falls very close to the borderline should serve as a reminder to all Members who may have occasion to initiate parliamentary proceedings, that they should be cautious in doing so on matters which touch their registrable interests, and should first seek the advice of the Commissioner or the Registrar of Members' interests."
They also ruled that Mr Dorrell should have declared his interest in the April debate.
The idea of Conservative frontbenchers being forced to clear their actions with an official before they are allowed to make a political move will dismay old hands in the Commons.
But the unanimous Standards and Privileges Committee decision to reverse Sir Gordon's ruling could also be read as a retreat from the standards introduced after Lord Nolan's 1995 parliamentary sleaze report.
Dennis MacShane, the Labour MP who laid the complaint against Mr Dorrell, said yesterday, however, that William Hague had to decide whether he wanted a full-time Opposition or "a part-time frontbench who will be constantly embarrassed as they decide whether it is more important to have nice little earners outside Parliament, which they will always have to declare when attacking the Government."
He released a list of 19 Conservative frontbenchers who had financial interests in firms which could have an impact on debates and questions they could be expected to raise in the House.
"From corner shops to energy prices, from property development to Asda, from insurance firms to private medicine, Mr Hague's team have their noses stuck deep in the extra-parliamentary trough.
"Hague has to clean up the Tory frontbench because more and more of them will be exposed when they initiate debates in the Commons."
Mr MacShane, who has already forced Mr Hague to switch Michael Fallon from his trade and industry team to the Treasury team after he neglected to declare an interest in the House on nursing homes, said he would be watching to make sure that Tory frontbenchers submitted themselves to Sir Gordon's prior restraint on their actions.Reuse content