The cleaning of London Underground is to be enhanced amid warnings that eight of the world's most dangerous superbugs exist on the network.

Industrial vacuum cleaners and magnetic wands will be used each night during the summer to remove metal particles, dust, oil and grease from around 50 stations and five tunnels.

An investigation published last month by London Metropolitan University and taxi insurers Staveley Head found 121 different types of bacteria and mould on public transport in the capital.

Eight of the most threatening bacteria to human health were discovered on the Tube, with the Victoria line deemed to be the dirtiest route.

The expanded cleaning regime is one of a series of measures announced by mayor Sadiq Khan as part of a new air quality action plan.

Tests will be carried out at more than a dozen stations to monitor how dust levels change at various times and locations.

Information from an improved air quality monitoring programme will be published on the Transport for London (TfL) website.

Mr Khan said: "Tube staff and the millions of passengers who use the Underground regularly deserve to breathe the cleanest air possible.

"TfL's new Underground air quality programme will help ensure dust and particles are kept to an absolute minimum.

"But I want to leave no stone unturned and I've also asked for an updated scientific analysis of pollution on the Tube so we can fully assess the air quality levels and take appropriate measures to ensure that the air is clean."

The combination of friction from Tube trains running along rails, air ventilation and skin particles from passengers all contribute to dust on the Tube system.

A TfL-funded study in 2004 found that dust on the network did not pose a health risk but Mr Khan has asked TfL to commission an updated review of the evidence.

Advice will be sought from the Department of Health's independent expert Committee on the Medical Effects of Air Pollutants.

London Underground managing director Mark Wild said: "We have been monitoring dust levels on the Tube for many years and, through a wide range of measures, have ensured that particle levels are well within Health and Safety Executive guidelines.

"But as scientific understanding of the effects of particles develops, we are ensuring that we're both using the very latest research and that we're doing everything possible to keep the air underground clean for our customers and staff."