asdf writes:

And to add to the misery, the Welwyn services are bustituted this
Sunday morning, and the Hertford services for the whole day.

That is bad. Surely the planned work should be postponed because of
the Pic line problems. Before he retired, my father worked for BR Civil
Engineers department. It was not unknown for planned engineering
possessions to be postponed or cancelled because of problems elsewhere
on the network.