I'm sure the ex and current squaddies on here can tell tales of far worse conditions we've had to endure over the years however, those sleeping arrangements are crap by any reasonable standard.
It's not like the PSU cops have had to dash down south cos London is on fire, This visit and therefore all of the logistics are pre planned. This being the case, hundreds of camp beds in a school gym is simply not acceptable particularly when you consider there will be people coming and going all day and night out of there..... the lights will be on all the time, it will be noisy due to the volume of people in the room, and hot.
It's not a deployment to some far flung craphole, it's a mutual aid deployment to a first world capital city.
As for the overtime, most will have had their rest days cancelled more than 15 days ago so will simply get a day back for working them. There will be overtime for working longer shifts but it certainly won't be 'shitloads'. Unless of course it kicks off and they earn their time and a third getting bricks chucked at them.