David Cameron has been told he should have kicked eurosceptic Tory MPs "in the balls" rather than indulging them.
Sir Nicholas Soames, one of the most pro-EU Conservative MPs, also said he knew "for a fact" that Boris Johnson did not really believe Britain should leave the EU.
In an interview with Conservative Home, Sir Nicholas said pro-Brexit MPs should have been stood up to.
“If you have an Alsatian sitting in front of you, and it growls at you and bares its teeth, there are two ways of dealing with it," he said.
"You can pat it on the head, in which case it’ll bite you, or you can kick it really hard in the balls, in which case it’ll run away.
"Successive Prime Ministers, and it’s not the present Prime Minister alone, have never understood that they have to take these people on."
“Kick it really hard in the balls”
- Tory MP Sir Nicholas Soames on what to do to eurosceptics
Sir Nicholas, the grandson of Winston Churchill, has developed a habit of taking on eurosceptics directly on Twitter.
He told Tory colleague John Redwood to "bugger off" over demands backbenchers listen to party members when deciding which way to vote in the referendum.
And he described Nigel Farage as "Donald Trump only without the charm" in another Twitter spat.