Not that unusual. Purdey sold many rifles that were supplied to them "in the white" so to speak, and then finished in their shop to some degree. Mostly you see rook rifles and other sub-best quality guns that fit this description. This one appears to be in that same line. Still looks like a high quality rifle, but it is probably not 100% Purdey built.

Contacting Purdey with the serial number should shed some light on it.

“I left long before daylight, alone but not lonely.”~Gordon Macquarrie