Thanks for this excellent information Gus, and apologies for the delayed response, as I've been away for a few days. (I'll be going away again next week on a clay plastering course - exciting times!)
Interesting what you say about the trial pitting - I thought doing a land investigation would help establish the best position for the house. The plot is about 10 miles inland and it hasn't been built on before. It was formerly part of a large estate, and is described as reasonably good agricultural land (3.2), so it's likely to be a mixture of clays. There are no watercourses running through it and there are houses built nearby. Also it's pretty flat which is always helpful!
At the moment I'm living near the coast and we do get battered by the westerly winds. I should probably spend some time at the plot with my anenometer checking the prevailing wind, which will probably be westerly.
I'll be getting help from Phil Christopher who has experience of working on cruck frame buildings so I think the main challenge will be convincing the planners. They usually like houses to be designed according to the "vernacular" but the vernacular from what century? Which time period are they trying to recapture? Hopefully they'll be open-minded!