Just wanted to say it was an excellent evening and many thanks to all who tried to pull my car out of the ditch after my 'unplanned detour'. I got home at 3:30am in the end. They rescued the car using a 36 tonne recovery vehicle with a crane. Once they got it off the concrete blocks that it had wedged on, the car wasn't too badly damaged. However, the hire car company wouldn't let me drive it, so I had to be taken to Leiceser to pick another one up, and then drive home from there in all the fog. Quite an eventful evening all in all.
Once again, thanks to all who tried to help, and I shall probably change my identity before the next one to avoid all the ribbing I'm going to get! LOL