I've booked this as a Triple-spotted Clay, but I wouldn't put a lot of money on it. It was all a quiver and keen for the off, so I had sent it on its way before it bashed itself to bits, and before reading that the colour of the hind wing is diagnostic. I'm pretty sure that the hind wing was light creamy brownish. The book says that the Double Square-spot has a greyer hind wing. However it seems quite early for a TS Clay which the book indicates appears rather later in the month.
I can always change the heading if someone knows better.
Someone did - and I have