My husband and son went last year with a couple of other chaps. Husband says:
"It's a flat grass field with pitches mown into the grass to show your space. Each area has a portakabin with washing up sinks, several toilet portakabins and some really good shower pods with lashings of hot water. There are cleaners on site 24/7 and do a great job keeping the facilities in top condition and far better than many campsites we've stayed on!
The English summer can cause all kinds of problems with mud, and getting stuck is a real problem to consider! The weather was great last year. It is not the camping area which is the problem, but there are limited access points which get carved up quickly as the site opens on Thursday and doesn't close until Monday. There are tractors to pull you out, but it's not ideal.
In 2017 there were three large camping fields, but the first two fields which are closest to the road fill up very quickly from Thursday lunchtime. If you are arriving after this time, it is something to bear in mind with regard to getting out if it rains badly.
There are regular shuttle buses to the main gate but it is only a 10 minute walk and often quicker than waiting for the bus. The field we stayed in had a small marquee set up as a shop with basic milk, bread, sausages etc. There was also a caravan serving bacon rolls and cups of tea until just after lunchtime.
Remember this is an 'all comers' campsite and is certainly noisier and .. er .. 'wilder' than permanent campsites just the same as Silverstone or other motor races (!). It's good natured but noisy until well into the early hours, especially on the Friday and Saturday nights, so be prepared to take some earplugs!
Overall definitely recommended if you want to get the full value out of the Festival of Speed and don't forget to book early. If you want pictures we can put some up."
There you are, direct from the Horse's Mouth!