John Penrose warned No.10 against refusing to appoint an ethical adviser.
Lord Geidt, who was concerned about possible plans to violate WTO rules, resigned from his position on Wednesday evening.
It comes after months of speculation that Geidt might resign over the Partygate scandal.
Penrose, who resigned as the government’s anti-corruption tsar earlier this month argued that it would be a “big mistake” to scrap the role.
BASC establishes positions for lead ammunition consulting
Government Food Strategy slammed as “wholly inadequate” by campaigners warning of a “national food emergency”
The Weston-super-Mare MP told the BBC: “Well, I think that that would be potentially quite a big mistake. The point here is that you can obviously, and if they felt it was sensibly it might be useful to look at it, you can obviously change the role a bit but you shouldn’t be weakening the role if you are going to come up with a revised version as a successor to Lord Geidt, some new format, some new way of dealing with the issue.”
He argued that the “parameters” of the independent adviser on ministers’ interests job could be adapted but that Geidt’s former role should continue to exist.
“So by all means change the parameters but I don’t think you can weaken it, particularly at the moment.
“I just think 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 are serious about this. This is part of the reset, I would argue, which the prime minister has rightly said he wants to do after last week’s vote of no confidence, good for him. This would be a good way of being part of that then moving it forward.”
Shadow attorney general Emily Thornberry says the PM “doesn’t have a moral backbone”.
She suggested to LBC that voters would be concerned about Geidt’s decision to quit: “I think people care that they have a Prime Minister who is dishonest and who is happy to break the rules and who doesn’t have a moral backbone, just doesn’t, and keeps losing ethics advisers because he is not ethical. I think that matters.”
She went on: “What is important is that we have a Prime Minister who doesn’t seem to think that the rules apply to him and they do.”