5 gallon suggestions

Various rasboras, shrimp, dario dario

Elassoma (need live or frozen food, but no heater), Leptolucania ommata (no heater, not quite as picky an eater as elassoma but still may refuse flake), and Heterandria Formosa (a puny U.S livebearer which eats anything small enough and is VERY easy to work with).

+1 for Heterandria Formosa, a North American native, is the world's smallest livebearer, and hardy as heck, and will eat just about anything (except expensive fancy food I got just for them ). It's got subdued, but stately colors that don't distract from a tank, and a fearless-but-friendly personality. They can be stocked very densely, due to an exceptionally low bioload, and only give birth to one fry at a time...every day. It's pretty much the chihuahua of the fish world.

Thanks for the suggestions.
I would really like to get heterandria formosa but they dont seem to be available in the UK.

I see. Perhaps our humble natives should invade the motherland at some point :hihi: