The latest Great British Railway Journeys programme features Ashford to Sevenoaks and includes a visit to the Hitachi Javelin maintenance depot at Ashford.  You can watch it on BBC iPlayer at the following web address (or on your TV/smartphone etc…):

http://www.bbc.co.uk/iplayer/episode/b06z8ht0/great-british-railway-journeys-series-7-16-ashford-to-sevenoaks

Unfortunately Mr Portillo misses out the 2 best destinations on the line, Paddock Wood and Tonbridge, but interesting nonetheless!