Interesting point - can't find any relevant legislation, but fishermen discuss it on this forum, and a tackle shop owner states he is not allowed to sell maggots in plastic bags:
Im a keen angler and have bought live bait for years, I must admit they've always came in plastic tubs with air holes.
I suspect by selling them in bags you will be depriving them of air possibly reducing their longevity and freshness plus if its hot they will be very smelly and sweaty.