As a first guess, I'd say it is Acer 'Shindeshojo'
Heres a photo on Billys Fujiyama Garden web site:
http://www.fujiyamagarden.com/Shindeshojo.htmland heres another from that same great man (alias Whis4ey)
http://www.gardenbuddies.com/forum/messages/4310/1158669.htmlon the garden buddies forum (gets around, doesnt he
)
I have 'Shindeshojo' and I'd say it is without doubt the most interesting of 28 different named cultivars which I bought ( a few were for friends who shared the order, and some suffered "accidents")
The leaves change continually the whole season from spring to autumn. Unlike many of the other acers, there is never a period when it looks unattractive or uninteresting.
As in the lower photo in Billys web page, the plant has a tint of green evident in the pinkish foiliage. Its this hue which make this plant so special. It has smaller leaves than the Acer palmatum atrpurpureum varieties.
Ive a LOT of photos of my Shindeshojo at different stages. One day soon I'll pull them together. I'll find one for here.
Now, you've got my attention! You've been to Beth Chatto's garden!!!!
Theres a special section on the forum for Gardens in England. Perhaps, (please!) you could tell us more about your visit?