It has only been the last 25 years that manufacturers have been required to supply equipment with plugs fitted (where not inappropriate). How to wire a plug was taught to all pupils aged 14 when I was at school, so it should be the case that anyone over 39 is competent to do this (though, unfortunately, experience shows this is not always the case). But it's OTT/ unreasonable for the same manufacturers to now insist on a certificate from an NICIEC member when they used to make everyone fit their own plugs to their products.