We're still in transition so there's still no requirement to have a tow rating either to tow or to teach towing, even on an EASA licence. Any qualifications gained under the old system can be converted to the EASA equivalent.
So you can still get tow training at a non-ATO BGA club, with the club's approval you can then teach others how to tow.
CAA conversion guidance here (still refers to 2015, read as 2018.) I'd suggest an email to the BGA office to find out how to convert teaching to tow experience into an EASA qualification.