Spotted this one on Ebay UK in October 2020 - not sure what it sold for but unsirprisingly, as an early Cooper S, it was snbapped up very quickly. The seller at the time made the following comments in the advertisement suggesting this mini has a very interesting history:

It's an Austin Mini Cooper 1275 MKI and was built on the 11th May 1964 and despatched on the 29 May 1964. It was a special order West midlands police car demonstrator, so a very early S. The Mini had the coolest plate Ive seen 999 MOM but this left the Mini around 67 (I assume when it was decommissioned) when it was issued with its current age correct reg, Ive the original registration book confirming this. (the reg is on a Vauxhall Mariva in Birmingham, I am trying to find the owner as would be wonderful to have it back on the Mini)

being a Police Mini it left the factory in Monotone White and had factory options of a Fresh air heater, Twin Petrol Tanks, Oil cooler, Calibrated speedometer and 3.44 to 1 final Gear ratio.

The Mini had a high standard restoration around 25 years ago then went into a private collection where it sat until I pulled it out. Ive not yet washed the Mini off as it feels like part of it and Ive been unsure on what to do with it. The floors are spotless and the paint work looks great. This is a true piece of Mini history. The Mini Cooper Register know of the Mini and have confirmed it as being the police car and kindly shared a picture of it in its police state in 1964, which or course I can share also.