Nope, it's part of the registration process AFTER BIVA for cars .
You get a mandatory Q plate if modified ORIGINAL chassis or monococque , a mandatory Q plate if new chassis and proof of 2 major compoents from one donor or and AGE related ( to donor logbook) if using 2 major components , that is usually engine and box though can be front and rear axle or front and rear suspensions.
You can also get a a NEW reg is vehicle si all new except for one reconditioned part.
I have an age related on my pick up after passing commercial SVA and using a Cortina donor with V5C and new chassis.
Using 8 points system you can modify without needing BIVA . All info on our website
www.the-ace.org.ukI know my way round the car registration process ( I was married to the manager of the LO for 10 years ! )but never been involved with bikes /trikes. I presumed they'd use the same system.