I suspect the only reason PoBox/Veber are now filing a trademark is to pre-empt a challenge on the domain. They are just domain squatters who got hold of python.co.uk and now see it as investment -- possibly one of their last chances at surviving, seeing how they're rumoured to be £ 300k in debt.
http://www.nominet.org.uk/disputes/when-use-drs/policy-and-p...
You might have a case under 3c(ii).
Edit: By the way, Nominet themselves use (or used) mailman, which uses Python:
https://lists.nominet.org.uk/mailman/listinfo/nom-steer
So you might have some sympathy there.