Hard to tell from the view, but it appears to be a true frog, probably one of the species known to exist in the UK [Pelophylax and Rana]. Perhaps not a usual color form, but probably nothing "noteworthy".
The recorded species in the UK are:
Lithobates catesbeianus
Pelophylax kl. esculenta
Pelophylax ridibundus
possibly Pelophylax bedriagae [vicinity of London]
Pelophylax lessonae [possibly extinct but reintroduced]
Rana temporaria [native]