Some clubs are affiliated to thier regional association of model engineers and have members who are up to date on regulations for inspecting and testing boilers and issuing test certificates. Latest rumour I heard was that boilers below 3 bar/litres do not need a full certificate, but probably need an exemption chit to say so.
Looking a bit further down the forum main page there is a section devoted to steam – posting there might run you into someone who really does know – they might not bother looking at the beginners section, so your chance of a reply up here has been slim.