@budgenator, 'I found the Great Britain has 2 species of tree frogs and I suspect a tree frog would be more able to ride a koi bare-back than a real toad would'.....really, that's news to me!
Where was that info found please? I hope you don't mind me asking as I would be interested to read that! As far as I've ever been aware we have the common frog and in a tiny area of East Anglia, the pool frog. Our toads are common toad and natterjack toad. Our only other amphibians are, smooth, palmate and crested newts. Any other species isn't native and not recognised nationally as a U.K. dweller, that's not to say an escapee from a zoo or somewhere doesn't lurk the in UK's damp and dark undergrowth!
Sorry to swerve slightly off the main topic here, but I couldn't let this pass without finding out more.