I doubt if there's a thatcher uses the site but just in case - we live in a 10 yr old house with a thatched roof. Does it matter that the thatch is getting a lot of lichen (not moss)growing on it?
Thanks buildersmate I think you've helped me before. Your link doesn't suggest it's anything bad and we certainly won't be trying to scrape it off yet.
You could phone them for advice - it is a commercial site, but would probably give free information on the basis of trying to locate another potewntial future customer.