Due to the risks of contamination at the planned Spitalbrook site in Broxbourne, Hertfordshire, an alternative site, six miles south of the planned site, is now being investigated.

The current venue designs could largely be transferred and accommodated to the new site, given its similarity to Spitalbrook.

ODA chief executive David Higgins said: "Although the Spitalbrook site investigations are still continuing, the initial results indicate that the cost of cleaning up the land for this venue would be prohibitive given budget and time restrictions.

"We will continue to look at the Spitalbrook site but it is prudent to develop robust contingency plans at this stage. We have a very challenging timetable and it is important to take swift action when presented with problems."