Testing is tricky - I wouldn't waste $ on Genova - use Metametrix GI Effects because of the PCR testing. Protozoa is even tougher to detect use old techniques. PCR is the way.
I would think that you could treat with what you have and if it is giardia then it will go easily. If you got something else you might need to ramp it up with other drug combos. So maybe test if you can't get rid of them.
I used MagicPharma with no problems, although I had to buy a Visa prepaid card. Got the meds just fine, all packed in their original package. They ship from India. Hopefully England does not use the same prohibitions that Euro countries do. Buy you can get around that.