Thanks for the update. I rather went down a rabbit hole googling this, as I suspect SP and others did also?
There doesn't appear to be anything that says it is lawful and equally nothing that says it is, in itself, unlawful? It seems it is certainly something many people have done, but it seems inherently dangerous and as BR says I am sure you could be charged with something else if the Police decided to. I wouldn't want to risk the Insurance status either?
External Link/Members Only
External Link/Members OnlyTrailers drawn by motor cycles84.—(1) Save as provided in paragraph (2), no person shall use, or cause or permit to be used, on a road a motor cycle—
(a)drawing behind it more than one trailer;
(b)drawing behind it any trailer carrying a passenger;
(c)drawing behind it a trailer with an unladen weight exceeding 254 kg;
(d)with not more than 2 wheels, without a sidecar, and with an engine capacity which does not exceed 125 cc, drawing behind it any trailer; or
(e)with not more than 2 wheels, without a sidecar and with an engine capacity exceeding 125 cc, drawing behind it any trailer unless—
(i)the trailer has an overall width not exceeding 1 m;
(ii)the distance between the rear axle of the motor cycle and the rearmost part of the trailer does not exceed 2.5 m;
(iii)the motor cycle is clearly and indelibly marked in a conspicuous and readily accessible position with its kerbside weight;
(iv)the trailer is clearly and indelibly marked in a conspicuous and readily accessible position with its unladen weight; and
(v)the laden weight of the trailer does not exceed 150 kg or two thirds of the kerbside weight of the motor cycle, whichever is the less.
(2) The provisions of paragraph (1)(b), (d) and (e) do not apply if the trailer is a broken down motorcycle and one passenger is riding it.