The local electrician near to me said adding a fuse connection unit is ok as long as you do all the tests and paperwork. He also said he would show me what needed doing.
Which is also what i was told on the tavcom mains compliance training.
I was also told being competant is about showing you have done training and been shown and can show you can do all the tests.
You do need a meggar tester (thats a brand name) fluke also do one
If the site failed the earth test for instance you would need to abort untill a sparky had fixed any faults you found before your install
Adding a new circuit is also sparky land i.e fitting new cable to a new mcb
Also you cannot add to a circuit without a RCD
you have to test the RCD, which you have to test trip's correctly using your slighty expensive new toy (meggar or Fluke others are available)
This is all i have been told on a course or in person, I like to listen and make sure what i am going to do i do correctly. I now have a part p tester which is great, I checked my earth and RCD and they work fine so my flat should burn down yet unless i cook something
I suspect sparky's would like to keep doing even minor works as it's money in their pockets not yours