Northern Line commuters have been raising their eyebrows and holding their noses over a mysterious stench pervading their journeys to work.
The source of a foul odour at Kennington station has baffled passengers and sparked an investigation by Transport for London (TfL).
The 'yeasty' stench, also likened to the smell of vomit, has reportedly lingered for months, according to commuters who regularly use the station.
Some passengers have even said they can smell the pong when the train doors are closed.
Comedian Rachel Parris reported a “very strong” smell of sick. Others have likened the odour to raw sewage.
TfL is also mystified by the origin of the noxious scent. They said it was a question they “quite frankly don’t know the answer to” and that they are investigating.
Ms Parris tweeted: “Londoners; sorry to be gross but does anyone know why Kennington station now permanently smells of sick? Like, for months now? V strong? @TfL?”
Another local said: “It's so bad and been like this for months! How has no one worked out the reason why?!”
While a third added: “Yup, noticed it on Saturday too. A bit yeasty I thought? It's a smell I'm fine with due to having worked in a lab, but obviously realise is still pretty gross...”
In response, Transport for London tweeted: “It’s a good question and one which quite frankly we don’t know the answer to. We are still investigating and hope to have identified the source and a solution soon. Pease accept my apologies.”
They told another concerned commuter that engineers had been on site and that they were “working to get this matter resolved as soon as we can.”
In an official statement, they said: "We apologise to customers who may have experienced an unpleasant smell at Kennington Tube station recently. We are investigating the cause and will work to remove it as quickly as we can.”
