:-D
Sorry, there isn't a short simple one.
Antarmike showed me a book called "the Traffic Officers Companion" by Gordon Wilson. (ISBN 07106 25693) it contains all sorts of rules and regs and is quite good. plus the picture of a Locomotive looks a bit like an Explorer.
If the towing vehicle could be considered a locomotive.
"mechanically propelled vehicle not constructed itself to carry load other than equipment for propulsion, loose tools and loose equipment"
Motor Tractor UW not exceeding 7370kg
Light Locomotive UW 7320kg to 11690kg
Heavy Locomotive UW exceeding 11690kg
you are allowed a width up to 275cm, explorer front axle is 263cm, I presume Constructor is similar.
as a loco you are allowed 3 trailers, with some size retrictions as Mike pointed out.
you do get into maximum weight and length issues but there is an exemption for towing broken down vehicles so probably ok if it has a meadows:cool2::-D
If you go over width, length, weight you need to operate under STGO which is also covered in the book.
Best bet is to get a copy and be able to show to the best of your knowledge you are legal and the average copper will hopefully decide it's not worth the paperwork and go after some chavs instead:-D