During my M3W ownership I checked up when this subject was last under discussion. This is an excerpt from DVLA V796 concerning vehicle registration plates.
There are separate provisions for motorcycles and tricycles. Basically motorcycles registered after 1.9.2001 must only display a number plate at the rear of the vehicle. Motorcycles registered before 1.9.2001 can display a number plate at the front but are not required to. Tricycles derived from four wheeled bodies i.e. saloon cars must meet the normal requirements above whereas tricycles derived from motorcycles must meet the requirements for motorcycles.
Whilst the wording is clumsy I've seen reference elsewhere the definition refers to tricycles with enclosed bodywork and steering wheel.
While that is true and still current, unfortunately, it doesn't cross-reference to the MOT class system, so in the mind of the MOT tester doubt will still exist.
I think a link between the two would solve this.
This is a link to the current V796 document, which includes your quote :
https://assets.publishing.service.g...ion-numbers-and_number-plates-inf104.pdf
