The National Trust has announced that -
The summer Solstice observance at Avebury is expected to be very busy and there will be limited car parking as a result. From Wednesday 20 June until mid-afternoon on Friday 22 June there will be a temporary campsite alongside the car park opening at 9am on Wednesday 20 June and closing at 2pm on Friday 22 June.
There'll be less than one hundred tent spaces, allocated on a first come first served basis. They are expected to be in high demand. There'll be no camping available on the weekends either side of the Solstice.
More here.