Part P is a section in the building regs which covers electrical installations its not a qualification in itself. To be Part-P compliant you need to be a)Defined as a competant person b)Licensed through a self certification scheme ie Napit, NICEIC, Elecsa etc.
To define yourself as competant you must either have gained sufficent expereience throughout your working life and have the technical knowledge through years of working in the industry or gained industry recognised qualifications 2330,2381,2382 etc. Or ideally both of the above. To gain registration through a scheme such as ther ones mentioned above you must possess some sort of qualification but in general the 17th Edition seems to be the minimum requirement. Then you need public liability insurance of £2m+. Then you need a calibrated test equipment usually to the tune of £500 and then you need to know how to use it and test sufficently as not to put your customers at risk and ensure your work is to an acceptable standard. The industry has been watered down in recent years with fast track training courses offereing the gold at the end of the rainbow for a few grand. It takes years to become good at it now weeks yeah you might sit in a nice warm workshop and have a go with some tools and wires but they won't show you how to find faults in properties and diagnose potentially lethal problems. All they do is show you how to wire things up that it. What about cable calculations, thermal capacity, volt drop, rupture capacity etc all things which probably are never touched upon in these overnight dream factories.