As already mentioned, FCC do plenty. Saw this service toay, which leaves Luton as normal but once south of the river turns into a random stopping pattern to Bromley South.Some bizarre calling patterns on FCC services to / from Bedford during the peak
Some which skip-stop random stations north of St. Albans with little consistency as to where they stop.
Three northbounds during the evening peak which call at most stations between St. Pancras and St. Albans (even though they are all followed by an all stations St. Albans or Luton service).
Then there is the return working to Bedford which also misses out a few stations while in SET land and a few more north of Luton.