Yes, there were police Darts round here in 1960-63, usually hood down as the headroom wasn't wonderful for a big man wearing a hat otherwise. They had automatic transmission, which was a standard, but rarely taken up, option. I think Hertfordshire had them, but the ones we saw were Metropolitan (London) Police, like the one in the above photo.
They were good for nearly 130 m.p.h. (rather less hood down) which was quite fast for the time.
I had some Darts from 1966 onwards, but the police no longer had them.