I finally cracked it. Please all accept my apologies for weeks of every deteriorating performance and down time. I've been trying to crack the issue for probably a full week in total and have just found the tiny error on both RR and ARRSE that was causing the trouble. There is a small benefit in that effectively the whole back end of the site has had a thorough spring clean - tweaked, upgraded, fixed, polished - so we should be faster than ever. Until the next time of course.