As mentioned previously Grazon 90 is the one. I can vouch for its effectiveness- its a back pack product- Pastor is pretty much the same thing but for boom spraying. the licences mentioned are for application, not purchase.
I keep hearing that suppliers will be expected to only sell product to people who can supply a licence at time of purchase, but the logistics of this are horrendous and cant see it happening any time soon. I ought Grazon 90 the other day and was not asked for a licence.
Obviously you're not actually going to apply it yourself so all is good
intrigued as to precisely what species of creature eats nettles- a succession of goats and sheep, and pigs failed to stop our ever expanding nettles from pretty much blocking out the sun- Grazon 90 however !!!!