Well staff sickness it says on the CFMU web page... one presumes that for it to be closed then 2 out of the three ATCOs required to operate it at night (two working, one on a break) must have phoned in sick... leaving NATS to explain to the airlines that they dont have a policy (or the staff) for providing cover for sickness on nightshifts! It will be interesting to see where the early far east traffic goes to get into London!