Boris Johnson has admitted making mistakes in the handling of the Owen Paterson case as he risked a fresh clash with Tory MPs over plans to ban them from paid political consultancy work.

The Prime Minister’s relationship with his backbenchers has been strained since he ordered them to back a plan to block the suspension of Mr Paterson for breaching lobbying rules, only to make a U-turn following a backlash.

He is now pushing for a wider shake-up of Commons standards rules to curb MPs’ second jobs, which could lead to a further clash with backbenchers.

The sleaze row dominated a tetchy session of Prime Minister’s Questions, which saw Mr Johnson rebuked by Commons Speaker Sir Lindsay Hoyle.

The Prime Minister faced further questions about the situation when he faced the Liaison Committee of senior MPs.

He admitted the initial effort to shield Mr Paterson from immediate suspension to enable a review of his case and the disciplinary process had been an error.

“The intention genuinely was not to exonerate anybody, the intention was to see whether there was some way in which, on a cross-party basis, we could improve the system,” Mr Johnson said.

“In retrospect it was obviously, obviously mistaken to think we could conflate the two things and do I regret that decision? Yes I certainly do.”

Mr Paterson quit as an MP rather than face a vote on his suspension after the Government abandoned its bid to shield him from an immediate sanction.

Mr Johnson insisted he wanted to find a cross-party approach to the Westminster sleaze rows but became involved in spiky Commons exchanges with Labour leader Sir Keir Starmer.

He said he wanted a new approach based on “two key principles”: that MPs should focus on their job in Parliament and “no-one should exploit their position in order to advance the commercial interests of anybody else”.

But any attempt at forging an alliance across the House was undermined by Mr Johnson repeatedly questioning Sir Keir’s own outside earnings as a lawyer before he became party leader, during angry exchanges in the Commons.

Sir Keir’s entry in the register of interests shows he earned more than £25,000 for legal work during this Parliament, before he became Labour leader.

At Prime Minister’s Questions, Mr Johnson accused the Labour leader of “Mish-conduct” – a reference to talks Sir Keir had with legal giant Mishcon de Reya about a possible role in 2017.

The Speaker repeatedly ordered Mr Johnson to stop asking Sir Keir questions and said the exchanges had been “ill-tempered”, adding: “I need this House to gain respect but it starts by individuals showing respect for each other.”

Sir Keir said Mr Johnson’s refusal to fully apologise for his stance on the Paterson case showed he was “a coward, not a leader”.

He later withdrew his allegation that the Prime Minister was a “coward”.

MPs will vote later on a Labour motion on banning consultancies, and a proposed Government amendment, which the Opposition claimed waters down the proposals.

Mr Johnson will also face the Tory backbench 1922 Committee in a bid to repair relations with his MPs, some of whom are furious at attempts to curb their outside earnings.

Sir Geoffrey Clifton-Brown, treasurer of the committee, said there was “dissatisfaction” with the Prime Minister in the Tory ranks.

He told BBC Radio 4’s Today programme he had “no problem” with a ban on paid consultancy work, but going further could “deter a whole class of people” from entering politics.

“I think we all need to take a long, deep breath on this and get it right,” he said.

“There are two real aspects to it. One is how we represent our constituents. And the second is what sort of type of people we want in Parliament.

“Because if we ban all second jobs, I think you are going to deter a whole class of people who represent the business opportunities in this country.

“There is dissatisfaction on the backbenches and that is why the Prime Minister needs to make it very clear to members of Parliament what he expects from us.”

In response to a second Labour motion, the Government has agreed to publish details of coronavirus contracts awarded to Randox, one of the firms that paid Mr Paterson.

But MPs were told officials have been “unable to locate a formal note” of what was said during a call on April 9 2020 between then minister Lord Bethell, Randox and Mr Paterson, although “that doesn’t mean there isn’t one”.

There is also fresh scrutiny of the role of all-party parliamentary groups (APPGs) and the firms that provide support for them.

The Commons Committee on Standards launched an investigation into the groups in late 2020 and the BBC reported that an estimated £30 million had been poured into APPGs over the past five years, of which £6.4 million was donated by companies registered as lobbyists.