I'd be very surprised if that was the case however it's certainly possible that Thurrock Council could insist on motor sport provision. I'd think though that if it went to appeal I couldn't see the government planning inspector upholding that.
As far as i read it:
They made a new application which involved moving the stadium on to the site of the existing car park. This was abandoned and they then made an application to vary the existing permission by shortening the track and erecting new buildings etc.