Thanks to the wonderful people from @Sherlockology I have discovered that they used 222 Winter Berries by Jessica in the series.
This shade is now being taken out of production but can/could still be ordered at amazon.co.uk at a slightly reduced price, which I did. The price range is the same as OPI, Essie, China Glaze.
When it was delivered, there was a useful leaflet in the parcel with additional info on what to do with specific nail problems.
The polish itself is wonderful. It covers very well, one layer could be enough, I did apply 2 layers and it dries very fast, is of great quality and has a very luxurious and lush finish.
It's my first Jessica polish but I doubt it'll be my last (although I now have a nail polish embargo) ;-)