That is notifiable work. It has to be registered with and notified with the local authority. You can do it if you have the skill, knowledge and competence to do this and can convince LABC that you do (with respect, you do not. Judging from your questions above. If you do not know what TT is then you don't even get to the starting gate, that is the first thing you learn as even a junior electrician).
Your option is to use a registered electrician to carry out the work. As above. Get yourself an EICR done.
this report will tell you what MUST be done to bring your installation up to scratch.
It will also tell you what, if anything, is unsafe or dangerous. I'm sure you want to know that?
Get the report done on your installation, it'll cost you a couple of hundred notes. Then you can make a decision on how to proceed.
*HINT* don't use the electrician that does the report for the remedial work. Some can make work for themselves, if you know what I mean.......
Happy to help with the results of the condition report.