Tunnelling for HS2 halted as mysterious pool of bubbling foam appears – video

Work on HS2 was halted after a mysterious five-metre square pool of bubbling foam appeared above an area where tunnelling was being carried out in Ruislip, west London. Locals spoke of a 'sinkhole' but an HS2 spokesperson said it was a 'slurry pool'. HS2 said the foam had been cleared, but white foam was seen 24 hours later. Tunnelling has now resumed but the area has been cordoned off and an investigation is under way

• Work halted on HS2 after mystery pool of bubbling foam appears