You need to of course first complete your Nurse training; there are two routes, the Diploma or Degree. For the Diploma you need 5 GCSE's at grade A-C, for the Degree you will need to have A levels. The training in the UK is 3 years in duration. If your aim is to be a Nurse Practitioner, I would advise you to do the Degree. Now generally speaking after your initial training you can do another course at Bsc level(it's usually no more than a year long) In advanced practise, or a speciality area or do the actual 'Advanced Nurse Practitioner' Bsc/Msc. If I were you, I'd do the Msc, contact your local University who will advise you of the courses that are on offer.
If you want to be an actual practise Nurse at a Drs Surgery you'll have to generally get a Surgery to take you on, then they will send you away on separate training courses. For example in things like Gyneocology (so you can do smears etc) Asthma and diabetes managment etc. One of the senior partnetrs at my Drs surgery is trying to pursuade me to come and worth for them, but I've chosen to do the Msc in Cardiology, which I am half way through, I quite like the idea or being a practise Nurse...I think I chose the wrong course! But you can still be a practise Nurse without the actual Nurse Practitioner Degree/Msc, but Ideally, nowdays you would need to be working towards it and you would need your basic Nurse training to be at Degree level. This may differ where you live, I live in the South EastI know many surgerys who are taking on newly qualified Nurses (it's cheaper) and then sending them away on training course which enables them to do certain tasks required. If you live in the South East I have the tutor for the advanced practioner course's number if that's of any use?