West Park Dairy operated just a single creamery at Market Lavington in Wiltshire. They were taken over by Express Dairies in 1937 so would no longer be operating in 1947/48, although the tanks were still in existence and may have still been in their original livery.
Assuming there was a dispatching creamery somewhere on the Bude branch, I can see the tanks being tripped to Oakhampton and then worked through to Exeter. The following dairies were in operation around nationalisation and making use of rail tanks:
United Dairies
Cow and Gate
CWS
Express Dairies
Ambrosia
MMB
There was still some churn traffic at this date so it would not be out of the question to see GWR Siphons full of churns (or even a mix of both types of vehicles).