Does this mean UKTV have officially 'lost' the rights to the classic series?
I doubt UKTV ever had exclusivity. BBC Two showed a few serials c.1999 and BBC Four did in the mid-00s, when UK Gold and UKTV Drama were showing them respectively.
Yes, when the BBC (or any other broadcaster) sells a programme to a digital channel it doesn't remove their right to show it. There are many programmes that get shown on BBC channels that are also in the libraries of the likes of UKTV.