You can buy keto sticks in any chemist, but you don't really need them. Just stick to the diet. You will know if you are in ketosis if the hunger pangs subside and you get a funny taste in your mouth. Even if you are not ketosis, you still have to stick to the diet, and you will still lose weight. So what's the point of spending £6 on keto sticks?
Read the thread about ketosis on here.