Whilst John Major's comments are not wrong, they come too late.
The whole of Cameron's strategy, especially in recent weeks, is to flirt with exit as a way of making him look stronger in negotiations.
He also needs to adopt this position to reassure those in his own party who think he is not being demanding enough.
It should not be forgotten that this is an issue that has been festering away in the Conservative Party since Thatcher's days and was at a high point under John Major's premiership.
Sir John Major has warned David Cameron against "flirting" with leaving the EU "at a moment when the whole world is coming together". The former prime minister said Thursday's EU reform talks should not be regarded as "High Noon". And they "should not decide whether or not we remain inside the European Union", he told BBC Radio 4's Today.