Paul, as AA has pointed out the MAOTS (mobile air operations teams) are based at RAF Benson in Oxfordshire and will doubtless give you any information or guidance if there are any of them actually in the UK at the moment.
As you rightly infer, military helicopters don't operate to public transport rules but that doesn't mean that we want to take unneccessary risks on approach or departure, just that we can operate more flexibly if required.
I don't have the NATO LS size dimensions to hand but I know the MAOTs will - the circle of 1.5 times the overall turning dimensions I referred to is what a military helicopter dispersal is supposed to have to operate helis from and is a good starting point as you want to keep people well outside the disc until the crew are ready for emplane/deplane.
You may be better off in the long run complying with the BHAB guidelines though since SAR may well be privatised in the future and any Fire Service helicopters (an ambition of some) may have to operate to public transport rules in some conditions.