Actually Yurpeen rules for motorcycles towing trailers are much more limiting than in the US - indeed, are there any rules about motorcycle trailers in the US?
British law was changed a while ago to allow towing trailers and the maximum trailer weight
is 150kg/330lb or 2/3rds the bike's unladen weight
, whichever is less. However the more practical limitation is that the trailer may extend no more than 2.5m/8.2ft from the bike's rear axle
which severely limits the size of trailer and seems a pretty daft limitation since it stops the use of US-style long tongue trailers which are probably a good idea for bikes.