Owen Paterson, the Tory MP found to have committed an “egregious” breach of lobbying rules, will fight to clear his name and to avoid a 30-day suspension from the Commons that could trigger a byelection.

Paterson hopes to launch an appeal against parliament’s sleaze watchdog by seeking a judicial review of its decision, and it is likely other Tory MPs will aid him by voting against a motion to enforce it.

The former environment secretary was found on Tuesday to have breached paid advocacy rules, two years after the Guardian published documents revealing how he lobbied for two companies he was paid a total of up to £112,000 a year to advise – Randox and Lynn’s Country Foods.

Kathryn Stone, the parliamentary standards commissioner, concluded her investigation by finding that Paterson made three approaches to the Food Standards Agency (FSA) relating to Randox and the testing of antibiotics in milk; seven to the same agency concerning Lynn’s Country Foods; and four to ministers at the Department for International Development about Randox and blood testing technology.

A follow-up investigation by the standards committee, which contains MPs from different political parties including several Conservatives, revealed Paterson used his parliamentary office on at least 16 occasions for business meetings with his clients between October 2016 and February 2020. The committee also found he sent two letters relating to his business interests on taxpayer-funded Commons-headed notepaper and failed to uphold the seven “principles of public life”.

“No previous case of paid advocacy has seen so many breaches or such a clear pattern of behaviour in failing to separate private and public interests,” the committee said in its final report, which was unanimously endorsed by all its members – apart from Sir Bernard Jenkin, who recused himself given he is a close friend of Paterson’s.

Paterson, the MP for North Shropshire, was revealed to have emailed FSA officials in November 2016 and praised Randox’s “superior technology”, which the committee said was an attempt to “confer a benefit on Randox, to whom he was a paid consultant”. Other messages sent by him to the FSA in November 2017 promoting Lynn’s Country Foods were found to be potentially directly beneficial to the company.

The committee said Paterson should be suspended from the Commons for 30 sitting days, meaning a recall ballot would be triggered. This would mean that if 10% of his constituents signed a petition demanding a byelection, one would automatically be called.

Notionally, motions to censure politicians based on recommendations from the standards committee require a formal vote, but one is not normally called, and it goes through “on the nod”.

But Paterson said the investigation was biased and “offends against the basic standard of procedural fairness”, adding it played a “major role” in driving his wife, Rose, to kill herself last summer.

He said: “Parliament’s internal system of justice needs to operate properly within the principles of natural justice.” Paterson is expected to contest the committee and commissioner’s report when the government calls a vote on the floor of the Commons next week on adopting their findings.

One ally of Paterson’s said he had been “stitched up”. They told the Guardian: “He’s already lost everything. His reputation and seat are the only things he has left, so he’s going to fight this.”

The MP also said they were certain colleagues would join Paterson in voting against the motion to suspend him. They said the fact the commissioner and the committee had declined to take oral evidence from 17 witnesses was evidence of a dodgy investigation. However, the committee said it already had written statements from them.

Downing Street offered no direct criticism of Paterson, with Boris Johnson’s spokesman saying “the standards regime is a matter for the House of Commons” and that the prime minister was “mindful of the pain faced by the Paterson family”. The spokesman also refused to confirm he thought the standards commissioner and committee’s system of scrutinising MPs’ behaviour was fit for purpose.

Another veteran Conservative backbencher said Paterson’s lobbying “would have been fine, if he wasn’t being paid”, adding: “These rules are in place for a reason. What was he thinking?”