I've been several times with the family and we've thoroughly enjoyed it. It's a mini version of Stourpaine - lots of the exhibitors from Stourpaine stay on for it. It's free (but you are "encouraged" to buy raffle tickets), friendly and you don't have to walk five miles from where you've parked the car. I've bought files, reamers and big MT drills there at a very good price.
Berwick is about 2 miles south of the A30 between Salisbury and Shaftesbury.
A few details at
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I've no official connection with it but a couple of the organisers are friends.
Bob