Not so, the e-bike doing th controlling means it is one vehicle and not a legal one.
What if the front passenger-carrying etrike (pushed by "Magic Type II"[not strictly necessary]), contained an autonomous AI - not in direct communication or in any way controlled by the ebike's controller - this AI would have learned to maintain a journey compatible position, speed and direction to the ebike behind it. Two completely independent and legal vehicles, your honour... the etrike AI merely has an ebike fetish, and is free to learn new skills if it wishes, get a degree, job, mortgage, house, spawn new (initially, inexplicably) smaller AIs using spares etc. just like the rest of us.
Uniquely in British law all motorised vehicles are banned from public roads unless specifically permitted for each classified type. That permission is obtained by either type approval or an exemption under type approval law.
https://www.gov.uk/vehicle-approval/exemptions-from-vehicle-approval
Do all tracked vehicles have an exemption? I'm being silly of course but add a battery, motor, cotroller and a track and you've got an exemption?
Or would London cabbies find tracked erickshaws easier to get approved?
https://historygarage.com/strange-or-visionary-tracked-motorcycles-of-the-past/
All you would need to do with this, is weld on some seats and a beach umbrella:
https://www.bikesure.co.uk/bikesureblog/2017/03/50000-for-the-ultimate-go-anywhere-german-motorcycle.html
there is no permission for a powered trailer pushing or following pedelec. In fact there's are a tiny number such vehicles in Britain and the Netherlands operating under "under the radar" at users risk due to there being so little policing of pedelcs. Once again no chance of type approval without parliament passing new law first, though a short time limited trial might be permitted akin to the very restricted one for scooters at present.
So the only route to saving black cabbie jobs through use of push trailers, available for hire for use on any (probably black) bicycle, is to create a business plan>Attract massive Silicon Valley vulture capital>Float on stock market as an Initial Public Offering>Short the price of the usual rapid fall in stock value after the IPO>Hide the money made from shorting the IPO in the Canaries>Offer select UK gov officials a shady deal promoting electric push trailers designed to maim or kill fewer pedestrians, riders and drivers than escooters? The Black Cabbies can save their own jobs.