The European Aviation Safety Agency (EASA) is the organisation that regulates all aviation activity within Europe and it delegates authority for implementation of its regulations to National Aviation Authorities; in our case the UK Civil Aviation Authority (CAA).
To assure safety within the industry, engineering personnel are licensed in the same way as pilots and air traffic controllers. If suitably licensed, an engineer can certify the work that has been carried out on an aircraft and return it to service.
EASA Part-147 prescribes the training standards that an organisation has to achieve in order to be approved to deliver training and examinations against EASA Part-66.