The first qualifying session is Wednesday night traditionally and the tickets will be operative from then although they will get you onto the "inside" campsites from Monday onwards (or Sunday if you go under the fence - Smokie
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You see that's the sort of comment that gets us chaps a bad name.
Got onto the campsite through the front door on Sunday last year, without too much difficulty. The real problem was being completely dehydrated and hungry, L'pool Boys and Smokie were my salvation.
Shan't make the same mistake this year