From the House of Commons briefing paper no.07212 on the Referendum Bill
This Bill requires a referendum to be held on the question of the UK’s continued membership of the European Union (EU) before the end of 2017. It does not contain any requirement for the UK Government to implement the results of the referendum, nor set a time limit by which a vote to leave the EU should be implemented. Instead, this is a type of referendum known as pre-legislative or consultative, which enables the electorate to voice an opinion which then influences the Government in its policy decisions. The referendums held in Scotland, Wales and Northern Ireland in 1997 and 1998 are examples of this type, where opinion was tested before legislation was introduced. The UK does not have constitutional provisions which would require the results of a referendum to be implemented, unlike, for example, the Republic of Ireland, where the circumstances in which a binding referendum should be held are set out in its constitution.
This is the information on which MPs voted for the Bill. Note very well the bits in bold.
I can't give you a link to it as it comes as a downloaded pdf. but it's easy enough to search for on line.
I know exactly what was in Cameron's leaflet (heaven knows, I've had it quoted at me often enough) but he had no right whatsoever to make that statement. It was for Parliament to make, not the government.
In case you don't understand how our constitution works, there are three elements to it, the Crown, or Executive which is represented by the Government in Parliament, the Legislature, which is the House of Commons (and the Lords to a lesser extent) and the Judiciary. Leaving aside the Judiciary as irrelevant ATM, it is the legislature (Parliament) which has the sovereign power and it is able to legitimately oppose and curb the power of the Executive/Crown. Parliament is in control. The Executive (Crown) can make very, very few decisions without the approval of parliament/the legislature. Parliament cannot be overidden by the Executive. That's what we fought a bloody civil war and chopped off a king's head in the 17thC to establish, the supremacy of Parliament.
That's why Cameron had no constitutional right to promise that the referendum would be implemented; it was exceeding his powers as a minister of the Crown.
Now, many of you may be completely unaware that the referendum was advisory because it was not clearly put to the public as such, but it is an indisputable FACT