Coventry (West Mids) have a black Volvo S60 t4, dark grey Honda Accord Type R and silver Mondeo ST hatchback.

Whilst Warwickshire have Jag X-types (dark grey and blue) although some of these seem to be armed response vehicles. Careful on the A46 near Leamington, they normally use the bridge for speed guns and also A46 between Coventry Airport and Binley where they hide at night with motorbikes and cars. Warwickshire mobile speed van is a short wheelbase tranny.

CMPG (i.e. around M6 jct 6) had champagne grey 535i and red Skoda Octavia estate, the 1.8 T sports version.

Best or rather funniest unmarked police car I saw was on the tele recently on one of these sky documentaries where they were pursuing (with siren and lights) a ford focus. They lost it. I think this may have been linked to the fact that they were chasing it in an unmarked Chrysler Voyager diesel automatic which should not be too hard to out-run on a cycle. Would be great to see a XF police car though!

From the same tele programme it seems that Thames Valley use a Omega's in dark blue, dark grey and burgundy.

Put "UK police cars" into google and you will come up with some websites which just have pics of police cars. click on the tab for your local force area and you may pick up some pics of your local unmarked cars.