PS - Karl it's great to hear back from you. You sound like you're in a much better place than previously and I'm sure having the running and marathon to focus on is probably helping in some way to distract you from other events. Sounds like you're well on track for sub-3.45 with that 18 mile time! Well done!
There is a really useful road closures and diversion schedule on the website - I downloaded it and sent it to my Mum and Dad who are also planning on traveling across from Yorkshire that morning. The main roads around White City and the start of the route are closed from about 6am and the areas further out by Altrincham etc are closed from about 8am however there are plenty of good diversions in place so maybe have a look at that?
skd14 - is the Yelling plan based on timed runs or mileage specific? I think I looked at that one and really liked it but I couldn't quite figure out how you did runs based on being out for a specific time? Do you estimate how many miles that time would equate to on a certain pace and plan you route from that or literally run for half the time and turn around? I looked at quite a few plans which were time-based and it just seemed too complicated for my small brain to figure out!