Question about Who can do what and minor works certs

thank you all for the replies. im a qualified plumber (city and guilds / competent person scheme for plumbing) and currently undergoing acs training. The overlap of plumbing and electrics is common and I find the whole area such a grey area.  I have done some electrical training as part of my plumbing training but nobody can ever give me a clear answer on what we as plumbers can and can't do electrically.  The general approach of most people I have worked with and who have trained me is that we can wire into a fsu and also everthing down stream of that we can work on.  so wire centres, immersion etc are fair game. But  I am trying to find a definitive answer. It's extremely important to me to do things right.  It seems to be arguable when minor works certs are needed and to what they apply to. I know some eletricians who say one is needed for changing a broken light switch. If everytime I work on a central heating system electrical component such as a cylinder stat or zone valve or (once gas safe a boiler) I need an electrician too with me then thats okay i will do it right. Another example being a broken shower pump that is already on its own fsu. To replace like for like would take about 30 mins if correct water isolators are in place and then do I need an electrician to connect the 3 wires to fsu...is minor works needed? If it is I have to say there are alot, if not all plumbers who are not doing it by the book.

thank you all for the replies. im a qualified plumber (city and guilds / competent person scheme for plumbing) and currently undergoing acs training. The overlap of plumbing and electrics is common and I find the whole area such a grey area.  I have done some electrical training as part of my plumbing training but nobody can ever give me a clear answer on what we as plumbers can and can't do electrically.  The general approach of most people I have worked with and who have trained me is that we can wire into a fsu and also everthing down stream of that we can work on.  so wire centres, immersion etc are fair game. But  I am trying to find a definitive answer. It's extremely important to me to do things right.  It seems to be arguable when minor works certs are needed and to what they apply to. I know some eletricians who say one is needed for changing a broken light switch. If everytime I work on a central heating system electrical component such as a cylinder stat or zone valve or (once gas safe a boiler) I need an electrician too with me then thats okay i will do it right. Another example being a broken shower pump that is already on its own fsu. To replace like for like would take about 30 mins if correct water isolators are in place and then do I need an electrician to connect the 3 wires to fsu...is minor works needed? If it is I have to say there are alot, if not all plumbers who are not doing it by the book.