I think that probably the situation is reviewed each time, hopefully through SEN Operations discussing it with easyJet. The upgrade from Cat 4 to Cat 6 for fire cover is supposed to require only 30 minutes notice and SEN is H24 from an ATC aspect, so I suppose its more a matter of whether the ground handlers' contracts stipulate late working when required. I've never heard of UK Borders not being available if required but perhaps it can happen.