BA has a quote of movements that can be used at its discretion through each scheduling season (subject to the noise QC mentioned above). In reality these are supposed to be used for scheduled landings between 0430 and 0600 but as some of these do not get used (delays/cancellations/diversions etc) it can use them for occasional (sic) off schedule movements like this one. I gather the outbound flight was delayed due to no loaders being available which seems a poor send off for Capt Chris!