Chris Huhne's presence in the Cabinet while under investigation by police is a "problem", a senior Tory has warned.
However, Conservative Party vice-chairman Michael Fallon said people should wait to see whether the Energy Secretary is prosecuted before demanding his resignation.
The comments came after Essex Police confirmed it was investigating allegations that Mr Huhne asked ex-wife Vicky Pryce to accept a speeding penalty on his behalf.
As he arrived at his Eastleigh constituency earlier, the Liberal Democrat was challenged by journalists over whether he planned to quit.
Mr Huhne replied: "No, thank you very much."
Mr Fallon conceded that "any minister under police investigation is a problem for the Government".
"I think what's important is that we wait until any minister is actually charged," he went on. "When they are charged then obviously it's right that minister has to step aside. He hasn't been charged."
Mr Fallon also played down friction in the coalition, after Tory backbenchers apparently complained about "yellow b***ards" during a private meeting this week.
Lib Dem leader Nick Clegg was said to have written to David Cameron insisting he will withdraw support for controversial health reforms unless they are "substantially changed".
But Mr Fallon said: "These are the kind of tensions you get in a coalition... And there are obviously Conservative MPs who don't quite understand why if Liberal Democrats sign a Bill, vote for a Bill, they should suddenly turn around a few weeks later and say we are a little bit worried about it."