Unusual Frog

Does anyone know what type of frog this is?
It's 2-3 times bigger than our common frog

Looks like a marsh frog

That's what I thought but it seems a bit bright, I found pictures similar under striped frog but I don't know if that's a type of frog or just a description.
Saw them on Sunday at a nature reserve, have told the warden just incase they need removing.

Maybe its their mating season and they get brighter to attact a mate? dunno

He is almost definitely a marsh frog, and their colouring does change throughout their lives, and also varies from individual to individual I gather.

He can happily coexist with other froggies, but will compete for the same food. Slugs and things.

Thanks. I knew they had Marsh frogs in that area. I wonder how big is an expectable colony before they start impacting on other species

I don't know, but as they are quite a bit bigger than other British frogs then it follows that they will eat a lot more and possibly deplete the available food, especially in long dry spells such as we have experienced this year. However, they probably eat other things too that their smaller cousins cannot manage, so perhaps they can live side by side in large numbers?