Thanks but having suffered the problem for several months I know that!
Nothing I have found tells me how to prevent being shown adverts when, being slightly old fashioned and having bought the 'phone outright, brand new and unlocked, I think I ought to be able to choose whether I want to be shown an advert every time I unlock the damn thing!
Sure I can root it but that seems a) and awful lot of work and b) slightly risky and can cause problems in the future.
Judging by the lack of response here it would appear not many people suffer the problem.