You prove competence by completing the accs accreditation in the various sections - cooking appliances, meters and pipework, space heaters , tumble dryers, ducted air heaters , central heating upto 70 kw , water heaters , etc etc etc , made up of practical assessments and written exams in the form of over 100 multiple choice questions - the pass rate is 100% - fail any element practical or written and you get referred and you have to take that element again . This you have to do every 5 years or with my x employer every 4 years . On top of this you are assessed at regular intervals by safety control engineers and they take no prisoners. Fail to correctly identify a dangerous appliance or installation or leave a gas escape or cause injury to person or persons causing hospitalisation then your at the mercy of your employer, gas safe , hse and don’t forget the criminal justice system. Then there is your overall safety score which is also monitored and any indiscretions will leave you labelled as ( reason for concern ) and this can see your previous 12 months jobs being investigated. If you can maintain all of this over 5 10 15 30 years without incident then this is in my mind competency of the highest level ..How do you prove competency, you may have worked in a discipline for a number of years or taken and been given certificates from the made up organisations that have appeared since the use of the word competent in jargon written by the same organisations with competency registrations lists, none of this proves competency, just that you are a drone driven by the media to follow the heard, Lets look at the "IET Wiring Regulations" they have no legal standing as they are not legislated, have not been through the legal government process or issued by the "Secretary of State" they are a British Standard only which is a guidance document, if it can be demonstrated that you carried out your work to a higher standard then that covers the need and qualification of competent, never been tested in court, but would make a very interesting case study.