I have never heard of a tug course as such. All the tuggies I know at several gliding clubs acquired their skills by being a gliding club member and being shown the ropes, except for a very small number who started on their own initiative several decades ago - but I doubt if anyone would be able to be self taught these days.
There is a Super Cub at Stapleford, I believe, with a hook (used to be my gliding club's - Essex GC - and still occasionally tows). You could try there.
To be able to tow at any gliding site, however, you would need to be a member of that gliding club on some basis or other - temporary member at least.
Chris N.