The Hagen Mini master test kits are pretty good and are perfectly accurate for freshwater use. Aquatics online have them for £22, take a look here ---> Aquatics Online UK - Aquarium Supplies, Pond, Pumps, Filters, and liners -Hagen Aquarium Test Kits

Just one thing that I would advise is to replace the nitrate test-reagent every few months as it will go out-of-date.