Presumably round an ash tree they'd be mating and therefore high up. I was looking for egg-laying females low down on Blackthorn. Had another look yesterday. Nothing.
There are some not very friendly signs on the site, put up by the Homes and Communities Agency. I was speaking to a local about it, there is some dispute about ownership of the land and basically, the Agency want to build 2,500 homes on it. I don't think it's imminent at this stage but it sounds like the whole site might be lost eventually.
I might try Noar Hill, it's not too far away and it's on my to do list for next year anyway for Duke of Burgundy.