Leading Conservative Brexiteer Jacob Rees-Mogg has rejected speculation he is planning to challenge Theresa May for the party leadership.
"I wouldn't challenge Theresa May. That's a ridiculous idea. The prime minister has my full support," he told the BBC's Andrew Marr show.
"I don't wish to be prime minister," he added, saying his "only ambition" was to make Brexit happen.
He also defended his company's investments in Russia.
Mr Rees-Mogg has been highly critical of the prime minister's preferred option for customs arrangements with the EU and has questioned whether her government is still committed to delivering Brexit.
Mr Rees-Mogg said the UK had made "a lot of compromises" during Brexit negotiations with Brussels and "nothing has come back".
'Strong position'
But he added: "I am reassured in the last week. I think the government is still committed. But there are concerns, inevitably, about the way the negotiations are proceeding."
He also questioned claims this week by the head of HM Revenue and Customs, Jon Thompson, that his preferred customs option would cost businesses up to £20bn, saying that sounded like a "high figure".
Mr Rees-Mogg, who chairs an influential group of Brexiteer Tory MPs. the European Research Group, said remaining in some form of customs union with the EU for years after Brexitwhich some have suggested will be the outcome of the Brexit talkswould not be delivering on Brexit.
He did not believe Theresa May should walk away from Brexit negotiations, he added, but should instead threaten not to pay the £40bn "divorce bill" agreed with the EU in December.
"We should say quite clearly, if we don't get the trade deal we want, you don't get the money'. That's a very strong negotiating position", he told Andrew Marr.
He denied trying to tell the prime minister what to do, saying he was "very respectful" of her position, adding that she was the "most impressive and dutiful leader that this country has ever had".
Russian investments
Asked if he would back the PM even if she returned from Brussels with a deal he did not like, he said: "I will back the prime minister on delivering on the promises she made in the Conservative manifesto and in her various speeches."
And he rejected press speculation he was plotting a leadership challenge, saying his only ambition was to ensure "Brexit means Brexit" from the back benches.
As stated by the Mail on Sunday, Mr Rees-Mogg's company, Somerset Capital Management, which manages nearly £7.5bn on behalf of private investors and City institutions, "has interests in two Russian firms blacklisted by the United States and others which are controlled by oligarchs in President Vladimir Putin's inner circle".
Mr Rees Mogg said he no longer ran Somerset Capital Management's investments but, he added, its clients had asked the company to invest their money in "emerging markets".
"We have a fiduciary duty to them to invest it as well as we can in businesses that we think will do well, subject to the law of the land," he told Andrew Marr.
He added: "We can not run our investments on my political opinions. I think we should be much tougher on Russia. I think we should impose a level of sanctions that America has imposed on Russia."