The NPPL is a more restrictive version of the EASA PPL, and requires slightly less training, making it cheaper, it’s also very similar to the new LAPL.
The NPPL is slightly restrictive in that you can only use it in the UK although it will be possible to use it in some parts of France soon. It only requires 32 hours flying, and then a test which brings it up to 35 hours. The medical can be done by any doctor approved to do HGV medicals, and so it is much cheaper to obtain.
All licences can be upgraded
When you have the necessary hours, and additional training on Basic Instrument Flying and Radio Aids, you can take a flying test and upgrade to a full PPL if you wish to. You have to upgrade your medical as well but sometimes this is not possible if you have medical problems in which case you will not be able to upgrade your licence. If you do have medical issues it is a good idea to get the CAA class 2 medical before embarking on more advanced training. Although training is never a bad idea.