As of yesterday, Witney depot now operate the 853.
It seems as if this may not be the case for much longer as it looks like the 853 may, at least in its current form, soon cease to exist. From the VOSA Bus Service registrations ("BSR" hereafter) for the Western Traffic Area on 21-Jul-2022 come these two entries which suggest that a change first proposed sometime ago (I forget when: a year or two I think?) may soon take place:
PH0005863/88 Registered
THAMES TRANSIT LIMITED
Route: Curbridge to Oxford via. Witney
Service Number: S2
Service Type: Normal Stopping
Effective Date: 28 Aug 2022
PH0005863/87 Registered
THAMES TRANSIT LIMITED
Route: Cheltenham to Witney via Northleach
Service Number: S2
Service Type: Normal Stopping
Effective Date: 28 Aug 2022
Use of the VOSA BSR website's "export as CSV" option allows you to obtain more details. For both registrations it says, under the "Other details" column, "Change of timetable and service number."
On the subject of the S2, a look in the VOSA BSR for 20-Jul-2022 gives us this entry:
PH0005863/41 Cancelled
THAMES TRANSIT LIMITED
Route: Oxford to Carterton
Service Number: S2 (S2X, H2, S2)
Service Type: Normal Stopping
Effective Date: 28 Aug 2022
Further to which the next entries down are:
PH0005863/41 Cancelled
THAMES TRANSIT LIMITED
Route: Eynsham to Burford
Service Number: H2 (H2)
Service Type: Normal Stopping
Effective Date: 28 Aug 2022
PH0005863/16 Registered
THAMES TRANSIT LIMITED
Route: Oxford to Carterton via Witney
Service Number: S1 (S1, NS1)
Service Type: Normal Stopping
Effective Date: 28 Aug 2022
For these three the "Other details" column tells us:
PH0005863/41: Cancellation
PH0005863/85: Cancellation
PH0005863/16: Revised route and timetable (presumably to replace, at least in part, the S2
Changes have also been registered, also effective 28/08/2022, for a number of routes in Banbury and these are also given in the VOSA BSR for 20/07/2022. There will be a revised timetable for the B3 (Banbury Town Centre - Longford) while the B9 (Banbury Town Centre - Hardwick) is withdrawn. It seems that the Hardwick area of Banbury won't be without buses though as there is a registration for a Service B4 between Banbury Town Centre and Hardwick. It isn't clear if the B4 and B9 will run the same line of route but a search on Traveline for a B4 in Banbury brings up no search results which means that the B4 is a new route. The VOSA BSR search for 21/07/2022 brings up that, also from 28/08/2022, there will be a revised timetable for Banbury's B5 (Banbury Town Centre - Bretch Hill).
Lastly there is the withdrawal of Stagecoach Oxford's 14 & 14A routes (City Centre - JR Hospital) and also, in Abingdon, cancellation of Service 34 (Abingdon - Harwell Campus) and revisions to services 33 (Wallingford - Abingdon) and 41 (Abingdon - Abingdon) but I apologise if Stagecoach Oxford does not belong under Stagecoach West like Banbury does.
Hope this is of interest,
Dave