Work halted on HS2 after mystery pool of bubbling foam appears

Tunnelling stopped briefly after brown bubbling substance emerged from the ground on rugby pitch in Ruislip

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, to the west of London, 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.