London buses are infested with cockroaches, drivers have claimed.

The pests have been spotted aboard dozens of Transport for London (TfL) buses and in drivers' rest areas, prompting safety campaigners to brand the situation "untenable".

Transport bosses have now launched an investigation after London bus safety campaigners raised the issue in a letter, a year after The Telegraph first revealed the scale of the problem.

Passengers have also noticed the infestation. A student, Matilda O'Flaherty, 21, told The Telegraph this week that she saw two cockroaches during a journey on the number 17 bus in August.

Describing how one crawled out from a hole in the seat before crawling up her leg, she said: "It was so gross and it was about the size of my thumb."

One driver on route 159 found a cockroach in his drink and "ended up vomiting", he told the London Bus Forums group.

In a video recorded inside the vehicle, he said: "I went to take a sip from my drink and felt something in my mouth. I spat it out and saw it was a cockroach. I felt sick and ended up vomiting."

Elsewhere, the group named buses on routes 159, 345 and 55 as suffering from infestations.

Kevin Mustafa, a London bus safety campaigner, said it was more than an "occasional nuisance", with "many drivers describing infestations".

He told the BBC on Monday: "The current state is untenable for drivers who already face demanding working conditions.

"London bus drivers are reporting persistent issues with cockroaches and unsanitary conditions onboard their vehicles.

"This is not a matter of occasional nuisance. Many drivers describe infestations, and the situation is starting to pose real health, safety and wellbeing risks."

Cockroaches are typically associated with unhygienic environments, although the insects have also been reported plaguing NHS hospitals earlier this year.

Last year Mr Mustafa, the bus campaigner, claimed TfL's contracted bus operators were "not cleaning the buses properly" and that "at least once a week" he heard a report of insects aboard a vehicle.

A TfL spokesman said instances of cockroaches being reported aboard buses were "rare".

"We are committed to working together with operators to provide a clean environment for staff and customers.

"All buses are also cleaned every night before entering service and reports such as these are rare. We take any report seriously and are urgently investigating the specific incidents that have been raised.

"As with any reports, we will take appropriate action as part of the investigation, which can include taking buses out of service for inspection, deep cleans and treatment with specialist equipment if necessary.

"We would like to reassure staff that our operators would never take action against people raising concerns about welfare or safety and encourage any driver with concerns to contact their employer, their union, or contact us directly."

London buses are 'infested with cockroaches'