Yes it does - ultimately it's in the power of the PM (and Queen) but he/she would seek Parliamentary and the HoL approval - and therein lies the question of if and when it becomes enforced, the proposed 3 month hiatus that could see:
(i) a fellow EU member (Italy, France, The Neths, Denmark or Sweden asking for a referendum - and the change that this may trigger, especially concerning not Freedom of Movement but Freedom of Employment
(ii) the UK moving its benefit packages
(iii) Greece, or even worse as we would be pulled in, France (they owe us over Euros 250 bln, second to none
(iv) Other N-African/ME issues
(v) the US taking their EU trade deal off the table as it has significantly changed - now under review apparently
(vi) lesser so as an issue, what the SNP does - and Ireland, esp. over N.Ireland who may be 'twinned' with Scotland.
(vii) the resignation of plonkers like Junckers - who deserves to go after his undiplomatic rant yesterday.
There are many other factors that could be thrown in, but I could see a case of not invoking it. And the Irish went was it through 3 advisory referendums to get what the government wanted.
And, you know, Cameron could always be voted back into leader of the Tories and all that implies.