Having lived fairly locally (Salisbury) for many years, I have only ever seen this place spelt with a Y. So I had a look at the old maps, and found that in the SW England OS 25 inch 1873-1888 maps it is indeed "Chamberlain". However, all subsequent editions show it with a Y. They must have decided it was more up market!
On a historical note for those not familiar with the area, the area of Compton Chamberlayne and Fovant (the next village) was a vast military encampment in WWI. The regimental badges carved into the chalk downs overlooking the villages are very famous, and although some have been lost those remaining are restored and well worth a visit.
