Guido's found the draft referendum bill.
Obviously I don't have legal expertise, but to me I agree with Guido that there would be nothing wrong with that Bill. That is, as long as Britain is seen as a separate nation state, making its own laws. If the European Union gains statehood (and it better not) there could be a problem from how I see it.
If Lisbon is ratified, de-ratifying it......is it a treaty, or is it a constitutional document?