I urge people not to read too much into media regards police response! From my perspective (10 years) there's likely to have been a lot going on around that time of day for any police service and no doubt Gatwick's ARV's were closest/closest available unit. Between 7-9 (on a late) is a cracking break time for a uniform patrol cop.
I'd be shocked if the officers went on board with firearms deployed, no doubt rifles were stowed in vehicle safe and they had Glocks on their legs/tasers on vests.
Handcuffs - officer's personal responsibility; resulting in a "use of force" form at the end of the shift. Depends how FO was transported to custody, if he sat in the back of the ARV then I'd say handcuffs were a 100% due to him being an unknown entity (be it unstable through alcohol or medically and the fact he likely has no criminal record to speak of).
From a speculative POV (and I have no idea how they board this type of flight at Gatwick). At my airfield a 777 is boarded via air bridge through door 2nd door just forward of the wing - if this is the case - I'm surprised no video has emerged of the arrest/intervention...unless the Police were more discreet than people think.