According to Jim Bradbury ("The Battle of Hastings"), the archers in pre-conquest England tended to come from the north countries; at least, it is from those territories that most mention (little enough anyway) of bows comes. Later, the Andresweald forest (that same woods at Harold's back during Hastings) is mentioned as having a reputation for archery.

It seems evident to me, via the Bayeux Tapestry, that the Norman infantry were the main influence upon English archery tradition, which reached its greatest development by the time of the Scottish wars of independence and the reign of Edward I. What the nature of that development was, nobody now knows much about it.

The bow was also an arm of significance in Viking armies; and the Welsh had a powerful bow, but the early illustrations of it make it out to be a stiff, thick shortbow, not a longbow. The bows on the Bayeux Tapestry also seem to be shortbows. I think it is likely that the artwork is distorted and at fault. For all extant bows found (very few indeed) tend to the longbow in proportion.

It is likely that the longbow was the natural development of the weapon once it was no longer used as primarily a hunting weapon: for a shortbow is the best in woods, and the longbow is best in efficiency without requiring a greater draw weight: the longer limbs store the flexed energy better, being capable of being drawn back further, thus imparting greater energy to the arrow for the same amount of draw weight. This average draw weight for an average archer was c. fifty pounds; for the higher draw weight of seventy pounds, far fewer men would be capable of managing efficiently in an extended battle without tiring. It appears that the English archers of the Hundred Years War drew the seventy pound bow, i.e. they were the pick of the lot, leaving the main mass of archers at home with their fifty pound bows.

Why do I know this? Because a coauthor and friend who is very savvy in physics maths has done the studies on where people died in battles like Crécy, Agincourt and Barnet; and he has determined that the energy of the bows used is indicated by where the enemy troops started to be killed, i.e. at what ranges from the line of archers: in the Hundred Years War the French die further out, and in the War of the Roses the killing range is reduced noticably, indicating that the average draw weight was less in the War of the Roses; i.e. longbowmen at home were including the range of bows available, and not just a hand-picked elite who could draw the seventy pound (and upwards) longbow.

We used this research in our wargaming rules The Art of War, to make our missile effects combat tables work according to the historical weapons. In other words, it wasn't just guesswork alone, but educated guesswork (if that makes it any better).