Well, constitutional expert Dr Alan Renwick said that it would be "very difficult to have a second referendum on this issue".
Talking to BBC's The World at One, Renwick said that while in principle the UK parliament can hold a referendum on pretty much anything it likes, it can't hold a "meaningful referendum on a deal, if there isn't a deal".
"The problem is with a second referendum is that there is a process that takes place once a country decides to leave the EU, as laid out in the Lisbon Treaty," he added. "So, if the Prime Minister declares the UK wants to leave the EU, that's followed by a negotiation between member states on the terms of Brexit, not on the terms of having some sort of better form of negotiated membership."
Those who favour Brexit may be tempted to come back and suggest that Cameron wouldn't necessarily need to trigger Article 50.
Article 50 gives the UK two years to negotiate an alternative relationship with the EU, after which the EU treaties shall no longer apply to the UK.
Bernard Jenkins, a pro-Out Conservative MP, earlier urged the Prime Minister not to "bind himself" to the framework of Article 50, saying there are other ways to leave. He echoes Vote Leave, which have already said: "We do not necessarily have to use Article 50 - we may agree with the EU another path that is in both our interests."
But the Prime Minister said Article 50 is the only way to exit the EU. He's then in agreement with Renwick, who said it is politically untenable not to use Article 50.
The discussion comes after Cameron today rejected the idea that the UK could vote to leave the UK and use that position to attempt to launch another renegotiation process and referendum.