I've always used Grazeon 90. Not sure if you need a license - doesn't say anything on the bottle & the guy in the shop didn't say anything... Works really well. I spray mine cos I've only got 2.5 acres for 2 horses, so I have to make every square inch count!
We normally let the donkeys eat them, but began getting over run, so srayed them this year. We also bought Grazon 90 with no problems, but strictly, it should only be sold to Licenced contractors/farmers. Wether or not you can buy it will depend on how strict the sellers are. Did work a treat though
PS. I think you are probably too late for this year now.
If winter paddocks, does it matter? Dont they die down over the winter anyway? Id probably just pull them out by hand (with gloves) and give them to the horses to eat!