From 'History of Woad in Britain':
"Woad was not used only for textile dyes and, for example the illustrators of the Lindisfarne Gospels (late 7th/early 8th century) used a woad-based pigment for the blue. Evidence for use of dyestuffs and vegetative remains of woad plants were found in Viking age York (9th/10th century).
By 1377, Coventry was apparently the fourth largest city in England, a centre of the wool and cloth trade. Blue cloth dyed in Coventry had a reputation for being highly colourfast, i.e. not fading with either washing or exposure to light. The phrase ‘as true as Coventry blue’ originated from this fact, as recorded by John Ray in 1670. The chief commodity imported into Coventry through Southampton from the late 1420s to 1478 was woad for dyeing the Coventry blue cloth.
Woad was used in England throughout the medieval period, much of it imported from Europe. However, the area under woad increased substantially during the 16th century. This was probably because woad supplies from abroad became unreliable and expensive.
Woad cultivation became strictly regulated in the late 1500s in a period of food shortage leading up to the famine of 1586 and concerns that too much land was being devoted to woad rather than to cereals. Queen Elizabeth I issued a “Proclamation against the sowing of woade” on 14 October 1585, stating that the breaking up and sowing of the most fertile ground with woad was a cause of great complaint and that no person was to break up ground for the present nor to sow woad within four miles of a market or clothing town or within eight miles of any house of the Queen’s. This was amended in 1587 to allow no more than 40 or 60 acres of woad in any one parish and no more than 20 acres sown by one person yearly."