You can tow on L-plates practicing for B+E.
"You are permitted to practice, on the road, with a laden or unladen trailer provided you display ‘L’ plates to the front and rear of the towing vehicle and trailer and are accompanied by a person who has either passed their driving test pre-1997, or held their ‘B+E’ licence for over three years."
And a 'B' can tow a trailer & load exceeding 750kgs.
All the info you need is in the sticky at the top of this section, ROG is the man!
Requirements for towing trailers in Great Britain