Well, on the basis of this thread I have bought some of the nivea factor 50 stuff today, but also got some simple factor 50 whilst I was there because it looks reasonable sun-blocky-ness-wise, claims to be suitable for sensitive skin, felt OK and smelt reasonable - a rare combination, I find. Will have to wait and see if either of them beings me out in a rash!
BTW, PolarBear, they had bottles of banana boat factor 30 kids lotion in Superdrug - the not spray stuff. I think they had factor 50 too, but by that point I was getting to the 'it's all blurring together' stage of bottle reading and had to run away.
And all the brands were on BOGOF everywhere. As per usual!