Passengers are causing severe delays to buses and trains by continuing to poo and vomit in them, transport bosses say.
Anti-social mess, including vomit, urine and blood, is being left on buses for staff to clean.
Transport for London (TfL) buses alone were reported as "soiled" a total of 14,632 times in 2018.
It classes a bus as having been soiled when passengers have left vomit, urine, blood or smashed glass behind.
Several bus routes had vehicles soiled on average more than twice per week.
But the worst month for such offences was October, in which there were 1,351 instances.
In December, buses were soiled 1,349 times and July saw 1,291 cases as England strung together a series of wins in the World Cup knockout stages.
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The worst route was the number 25 bus between Ilford in east London and Holborn in the centre of the city.
John Murphy, regional officer of the Unite union, which represents cleaners on London buses, said: "If buses are soiled or fouled then that results in the bus being taken out of service which has the biggest impact on passengers who experience longer journeys and delays."
Tube trains also had to be delayed by at least two minutes on 801 separate occasions last year while staff cleaned up a "soiled car".
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A cleaner on the District and Central lines, who wishes to remain anonymous, said he and his colleagues face difficult working conditions.
He added: "Sometimes it is very disgusting, especially on weekends and nights.
"From my own experience, once I even found a poo on the train and you have to clean it properly."
Some passengers "don't care about the cleaners", he added.
The Northern line was the worst affected underground route, with 221 of the incidents in 2018 happening on the route which stops at nightlife hotspots including Old Street and Camden Town.
This was followed by the Jubilee (113), Central (101) and Piccadilly (90) lines.
