A lot of this is also discussed at www.lspace.org check out the Annoited Pratchett File (APF)
Nope. Scotland. This is clear from Lancre’s first appearance in Wyrd Sisters, which is a spoof of MacBeth, Shakespeare’s famous “Scottish play.” Also, there are all sorts of other fairies and godlings, like Herne the Hunted, the Pictsies (easily my favorite pun in all of Pratchett’s writing) or the Long Man, who are recognizable as British, if not specifically Scottish.