If you don't do a lot of notifiable work then joining a scheme is going to be an expensive thing to do - unless you find yourself with clients who impose restrictions*.
If you get asked to do notifiable work, just quote for it, and point out that it's the customer who is responsible for notifying the LABC dept before work starts and paying whatever the LABC requires. As long as you point that out in writing in your quote, you are in the clear if the customer "forgets" to do it.
* One example is that under Church of England standing rules, the PCC (Parochial Church Council) is only supposed to employ electricians who are members of an approved scheme. I can sort of understand that since it sort-of outsources the task of filtering electricians based on ability and removed the liability from (generally very non-technical) PCC members of having to figure out if a trade they are planning to employ is "competent". But of course, we all know how well the schemes enforce standards as long as they get their membership fees. Our PCC decided to take a "flexible" view on the requirements - allowing me to sort out the mess they had while I was "between employers", covering the costs of my insurance and a bit of pocket money.