Kamagra is simply an Indian manufacturers trade name for Sildenafil, which is the generic name for Viagra
No-one has a UK licence to sell pharmaceuticals containing / branded as Kamagra. It follows that any you see have either been directly imported by the user, or imported illegally. It further follows that no UK quality checks will have been carried out. While a lot of Kamagra imported is OK, there is no way a buyer can check if what he is getting is correctly formulated or not.