If you book one of the NCP car parks, make sure you check out google street view to find out _exactly_ where it is.
After getting up at 3am, I ended up in Whitechapel driving round the block a few times until I saw the NCP car park was through an archway in a terrace of shops with a tiny sign inside the arch!
Also, I drove in through the west end, they were closing the roads off pretty much after I drove through.
Once you get going, enjoy the closed roads and remember to keep eating. Road biking is less effort than mountain biking but if you don’t eat you’ll bonk after 2 hours. You’ll be fine :)