In what is being seen as his strongest message yet on Europe, Cameron will say: “Earlier this week I made clear I would not lead a government that either could not or did not deliver an in/out referendum.
“Let me be absolutely clear. The British people need to have their say on our membership of the EU. For me this is a fundamental principle. And I would not be Prime Minister of a government unless we could carry out our pledge of an in-out referendum.”
Critics have accused Cameron of dithering over Europe and of failing to deliver his referendum promise, first made to voters in 2009.