A shocking video shows a bucket full of black sludge extracted from just four seats on the London Underground by a cleaner.
He posted the footage as a publicity stunt for his company, but viewers were left horrified by the grimy truth of Tube seats.
Steven James – also known as Mr Carpet Clean – filmed himself power-washing the seats on a Northern Line train at Camden Town station.
He then goes in with an electronic carpet cleaner to get out the more deeply embedded dirt.
But the real shock comes when he shows the yellow bucket filled with murky water and grime.
He is heard saying: ‘Health warning. Where do you go after travelling on the Underground?’
Disgusted viewers replied, calling the seats ‘absolutely filthy’ and saying that is the reason they take off their ‘outside clothes’ as soon as they get home.
One comment said they ‘always stand’ because they’re afraid of how dirty the seats could be.
Speaking to the BBC, Mr James said that seeing the resulting sludge was ‘the pinnacle of the therapeutic side’ of cleaning.
But Transport for London claimed he was putting other passengers at risk by emptying a bucket of water near a live rail.
It said the activity was dangerous and put both the cleaner and those around him at risk of harm.
Mr James said ‘I definitely didn’t put anyone at risk’ but warned viewers that they shouldn’t attempt to clean the seats themselves.
‘I won’t be doing that again,’ he added.
A TfL Spokesperson said: ‘Our cleaning schedule for Tube trains consists of two different levels of cleaning: pre-service cleans (daily), and a deep clean of the interior and exterior of the train around every 28 days.
‘All floors and surfaces are cleaned daily on every train as part of the pre-service clean. Seats are inspected and cleaned as required during this pre-service clean, with further cleaning as part of the deep clean.’