Nigel,
You should also get details if you look at the Sacrewell Farm website.
As NDIY says, Sacrewell is a left turn, about 300 yards to the EAST of the two roundabouts where the A47 and A1 junctions. If you are heading west, you need to go round the first roundabout to turn east.
The lower field will be mostly Traction Engines, but there will be other exhibits, the static ones will mostly be in the Barn, which, this year, probably means that you will need to brass up as you go through Reception. (New farm management)
Look forward to seeing you there! (most of the time, I'll be up in the barn)
Howard