Haven't found specifically where it is today, unless it is still owned by Sauders. I'm not sure if the Rolls shown in the opening credits is the same car actually used in the series. There are some online references saying Audrey's car was a 1930 Phantom.
1934 Rolls Royce 20/25 - As seen in 'The Captains Car' (BBC TV - 1975), this is the Mayor's car. This splendid 4 Door 3 Light saloon is owned by Brian Saunders of Enfield. The vehicle also appeared in 'To The Manor Born', in the opening credits.
home.btconnect.com/howejam/dadsarmy/motors/motors_tv_rollsroyce2025.htm no longer exists
dadsarmy.retrospace.co.uk/motors/motors_tv_rollsroyce2025.htm no longer exists
This is 20/25HP chassis #GRC33 with H.J.Mulliner saloon body. It also appeared in the "To the Manor Born" TV series. 1934 Rolls-Royce 20/25 h.p. H.J.Mulliner Saloon [GRC33]
http://www.imcdb.org/vehicle.php?id=179871&PHPSESSID=44aae6f0685ef469eee86fecd7b03b4c
[Don't know about the ghastly camouflage paint job, but the tag number is the same.]