Fizz, you're talking about Runner's retreat. I paid for that, and it was very well worth it. You get a private bag check, so when it started sleeting we all grabbed our bags back so we could wear more layers for the race
Also it has private loos (which means much shorter queues).
The best bit was the free hot choclate/coffee/tea to warm up before and after the race.
Runner's retreat will be available online later this year on the same area you used to register for the race itself.
For those who are hiring a car, the other option is to stay in the car until just before the race starts.
RB, what other questions do you have, I'm sure someone will know the answer.