Surveys of the Olympic sites in Stratford have revealed a 10 acre swathe of Japanese knotweed where the velodrome and aquatic centre are to be built.

Clearing the invasive weed, which if left could undermine stadium walls an crack concrete concourses, could cost the Olympic Delivery Authority as much as £70m.

This is in addition to the clean-up of identified contamination of mercury, lead and petrochemicals in the soil, asbestos in derelict buildings andd unexploded Worldd War II bombs.

However, the ODA insists that the remediation of the Olympic site is on schedule and the costs are within the £220m budget.

Sunday Times