Thank you all so much for your replies, I wasn't expecting such a great response.
Knee height seems to have a reasonable consensus so that's pretty much what I did, about 20 inches, my thinking being I can easily lower it in the future if I want .
Made from locally grown Scottish larch milled by myself so so is minimal, 3" square posts in the ground, 5x2 cross pieces both ways (apart from one crosspiece as I ran out of larch) 2.6m long should give me loads of space for 2 hives. Can't see this blowing over even up here on the Isle of Mull where we get a LOT of weather
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