This MP is very difficult to pin down, especially as there is no record of a Dorchester burgess of this name. He may have been the man who at some point in the late 1420s sued a chaplain from Chideock in Dorset for wrongful detention of a book worth four marks. The chaplain was pardoned his outlawry for failing to make answer in November 1430.
The only factor linking this John atte Mille with the Dorchester MP is the coincidence of dating, in that while the Parliament of February-July 1449 was in being the Cheddar inheritance was subject to litigation in the courts at Westminster. It may also be significant that John atte Mille was named a collector in Somerset of the subsidies granted by the Commons in that same Parliament; and while MPs were generally successful in avoiding appointment as collectors in the constituencies they were representing, it was more difficult to escape appointment elsewhere.
