On Wed, 18 Apr 2007 12:32:00 +0100, Toby wrote:

If I have a ticket to Zone 2 whilst travelling southbound on the
Bedford-Brighton service, am I able to alight at Farringdon/City
Thameslink/Blackfriars/London Bridge, or must I alight at Kings Cross
Thameslink and catch the underground from there?

If your ticket is to U12, you may transfer to the Underground anywhere
between West Hampstead and Moorgate/Elephant & Castle/London Bridge
(except City Thameslink which isn't an official interchange with the
Tube, though you could still end your journey there). LU zonal fares
are valid on FCC between these stations.