Some pet stores will sell Advantage, I think, but Revolution is only through the vet. At least that's how it is in the US. In the UK, the brand names might be different as well. Advantage is imidacloprid and Revolution is selamectin. Ivermectin can be gotten in the US at farm supply stores but I don't personally recommend giving it without a vet's direct supervision because it can cause really bad reactions. Someone else may step in and tell you how to do that; or it may not be available in the UK.