Plans to cool the tube and upgrade stations are in doubt after the collapse of the Metronet consortium, it emerged this week.

Transport for London (TfL), which will take over maintenance of the lines early next year, said a £150m cooling system for the network was under review.

Groundwater cooling trials were carried out at Victoria station last year and extended to other stations this year. Further testing was expected next year, but may not go ahead.

Tim O’Toole, managing director of London Underground, told MPs earlier this month that TfL faced “very tough choices” after the collapse of Metronet.