Boris Johnson would be committing a “big mistake” if he refuses to replace Lord Geidt as ethics adviser, the Prime Minister’s former anti-corruption champion has warned.

Conservative former minister John Penrose said on Friday that a failure to fill the role after Lord Geidt’s resignation in anger would leave “really quite damaging questions dangling”.

Committee on Standards in Public Life chairman Lord Evans issued a warning that “removing this independent voice on standards issues at the heart of Government would risk further damage to public perceptions of standards”.

Lord Geidt said he had been narrowly clinging on as ministerial interests adviser over partygate but ultimately quit after being forced into an “impossible and odious” position by the Prime Minister.

He accused Mr Johnson of considering risking a “deliberate and purposeful breach” of his own ministerial code by potentially breaking World Trade Organisation rules over Chinese steel tariffs.

Downing Street accepted the ethics chief fulfils a “vitally important” function advising on the ministerial code but said the Prime Minister was reviewing the position and could abolish it.

But on Friday Number 10 refused to commit to completing its review before the end of the year.

Mr Penrose warned of the effect of abolishing the position, telling BBC Radio 4’s Today programme: “I think that would be potentially quite a big mistake.”

“I think one of the reasons why it’s important to have some continuity, why it’s important to have if not a precise replacement then an effective succession here, is to make sure that you don’t leave really quite damaging questions dangling and that anything that’s outstanding doesn’t just get forgotten and lost,” he added.

The MP for Weston-super-Mare resigned from the anti-corruption role last week accusing Mr Johnson of breaking the code in his response to Sue Gray’s report into lockdown-breaking parties.

On Friday, Mr Penrose added: “I just think that the Prime Minister is currently overdrawn, if I can put it that way, on his account with both the voters and with the parliamentary party. They need to show that they’re serious about this.”

Lord Evans, the chair of the standards watchdog, also warned against failing to replace Lord Geidt.

“At a time of heightened concern about standards in public life, any change to the oversight of ministerial behaviour must be stronger, not weaker, than we have now,” he wrote online.

Downing Street defended the review, insisting that the Prime Minister will take advice from those within No 10 as well as “others with expertise in this area”.

“And it may be that the Prime Minister decides to make a like-for-like replacement, or it might be that we set up a different body that undertakes the same functions,” a No 10 spokesman said.

“But the Prime Minister thinks it’s right to take the time to reflect on those issues which are well highlighted.”

But he declined to commit to the review being completed within the year, telling reporters: “I wouldn’t get into timelines.”

In 2020, Sir Alex Allan was the first of Mr Johnson’s ethics advisers to resign after the Prime Minister refused to accept his finding that Home Secretary Priti Patel bullied civil servants.

It was five months before he was replaced, and in that instance there was no review of whether the position should exist or not.

Sir Alex backed Lord Geidt’s resignation as principled, arguing that the trade policy disagreement was the tipping point after a series of scandals including Mr Johnson being fined by police for breaking coronavirus laws.

He told BBC Newscast: “I think this was the final straw coming on top of, for example, his concerns about the fact the Prime Minister hadn’t said anything about the Ministerial Code in all of his explanations of the partygate saga.”

Labour has also demanded a direct replacement for Lord Geidt and the FDA union representing civil servants warned that the code is the only way workers can raises complaints of misconduct, bullying or sexual harassment against ministers.