Here's a prime slice of Marvel UK cheese: a promotion for their Summer 1975 promotion (although, according to my notes the advert ran in a comic cover-dated 13 September which - if that note's right - means their production department had got themselves into a muddle): a Marvel mask! Ahem.
It's a bit of a cheat... they weren't even free masks. As the BLUE PETER inspired (not really) instructions suggest, the masks were just printed in the comics themselves and readers were expected to attach them to cardboard. Cheap is cheap.
But it does neatly summarise the UK line at that moment... it's not hard to guess which mask design was printed in which of the weeklies.