If you have to have an English gun the old adage of "beggars can't be choosy" applies. Very few 20 gauge guns were turned out by the Brits and if they are in good condition a significant premium is attached to them. Most English guns were built "in the trade" that is, by outworkers. So, it would be difficult to point to any one maker and say you should try to buy his. In other words, every maker was capable of offering a "best" gun and also a low priced gun. My suggestion: if you find a 20 gauge, let the gun be judged on its own merits, not by the name on the barrel.