Work on HS2 was halted on Saturday after a mysterious five-metre square pool of bubbling foam emerged above the ground where tunnelling was being carried out.
The area on a rugby pitch in Ruislip, in a west London borough, has been cordoned off, danger signs have been erected, and an investigation is under way. Local residents described it as a “sinkhole”, but a HS2 spokesperson said what had emerged from the ground was a slurry pool.
