We were recently in a Premier Inn when the fire alarm went off, the firebrigade had to attend (there was a fire in the kitchen), no head count was done and it was lucky that it wasn't, as part of our group was still at the wedding reception that we went for, one had copped off and wasn't coming back to the hotel until morning.
We walked straight over the MD's, with other guests.
The fire and head count thing doesn't happen, the guests names would have to be called, unless you think that single people don't book double rooms in case they get lucky and then another person is there.
There isn't fires that intense in the UK, unless it is a small rural hotel.
What you could do is phone the hotel and say that you need a double room, but if you were let down by a babysitter how would that effect the price.
Then say nothing if the price would go up.
Did you all not go through the partying stage, when you took sleeping bags and piled in one room?