Excellent.
Im fairly close at Tring so have easy access to M25 and M1.
South Mimms Services which is Jct23 M25, strikes me as a good point. Not long after that you will be getting on the M1. When you get on to the M1 you have Toddington Services.
Not sure what time we want to get to track? Toddington Services is approx. 50mins - 1hr from the track .
I can realistically be at either of above but Toddington would make more sense if others want to meet after South Mimms.