You can get Xenical (fat blocker) and Reductil (appetite suppresant) on prescription from most GPs. They may also be able to provide counselling, nutritional advice, gym "prescription" and in some cases I think they will fund commercial diets (Lipotrim was an NHS diet to start with I think and I know that the NHS has funded Weight-to-go for some people). It can really vary depending on the practice you are with though so if your GP is useless see if there is another one you can go to that gives better options. Some PCTs may also have hospital based weight loss functions that offer the full range of options, I know one of the London ones does. Also I think surgery is getting much more available on the NHS in most areas but it is a bit of a post code lottery.
The problem is often that an individual GP may have a particular attitude about weight loss or treatment that might not be helpful. Some don't believe in the drugs and some just say you have to eat less whilst not really understanding all the practical and emotional problems this presents. I would ask your GP what that particular practice provides and if that doesn't really suit you contact your local PCT and see if there are any other options in your area.