Railway bosses have apologised after passengers found themselves listening into pornography being played over a train's public address system.
Video posted on Twitter shows travellers giggling as the X-rated sounds filtered over the carriages' loudspeakers.
The blue broadcast – on an 11.30am service from Wandsworth Town to Clapham Junction – is thought to have occurred after a staff member accessed the adult material while a microphone was still live.
The moment was captured for posterity by Twitter user Paul Brunton, who recorded the carriage’s reaction and posted it online.
"Is that coming from the driver?" one women can be heard asking in disbelief.
As if in reply, the film’s volume increases. “More,” its apparent protagonist grunts. “Oh…more.”
South Western Railway (SWR), which runs the service, immediately apologised and launched an investigation.
But many on social media appeared delighted with the faux pas. “At least someone's enjoying the commute to work," wrote one.
SWR released a statement saying: "South Western Railway has a policy of blocking inappropriate material, including pornographic websites, on its onboard and station Wi-Fi services.
"We are investigating this incident to establish how this material was broadcast on our service.
"Today’s incident is wholly unacceptable and we apologise to customers."
It came as guards and drivers at the company continued to hold occasional strikes in protest at plans to reduce the number of workers on trains.
