A £17m train has been put out of action after being covered "top to bottom" in graffiti.
Govia Thameslink Railway (GTR) said seven of 12 carriages were sprayed at sidings in West Worthing, West Sussex.
Helen Patterson, who filmed the damage to the Class 700 train in Bedford, where it will be repaired, said it had been "trashed" by "thugs".
British Transport Police said it was investigating the vandalism, which was reported on Wednesday.
The train company is currently under fire for cancelling services to deal with a new timetable that caused chaos on lines across the UK.
Ms Patterson, from Bedford, said in her commentary on the video, which was posted on Facebook: "I cannot believe they have done this.
"How much hassle have Thameslink commuters had in the past weeks and now this... it beggars belief."
A GTR spokesman said the train's carriages "were covered top to bottom in graffiti".
