Just a quick note a UK en-route sector is NEVER operated single staffed. A T and P is always on duty H24. To imply otherwise is just wrong.
Not everywhere, unless you mean Swanwick is the UK
And if a flow person came over to me and asked if i "could squeeze another one in to save them a delay" the answer would be a very quick and nasty two word answer. I'll do my job correctly by refusing and they should do theirs by not asking.
They could probably do it anyway without asking and you'd never know.
The monitor values are not a capacity figure with a glass ceiling. They are a value which 'triggers' the flow people to consider whether the demand can be managed or not by the system. They typically provide a 30% buffer below the probable ultimate capacity of the sector. So, as I say, if you are operating a sector with a monitor value of 30-40 an hour, you'd never notice that extra one unless you went and did a traffic count.
In units where the flow people are also valid controllers, they are well able to judge the complexity of the traffic demand, the capacity for the sector to handle a few extras based on the exact traffic situation and loading, and the abilities of the team who are providing the ATS. If they are not happy, then they'll regulate accordingly. But if the flow kit is showing a traffic flow with the sector at or near the volume, yet you are literally sitting twiddling your thumbs, they will get on with maximising the traffic flows without necessarily informing the sector team, provided they are confident there will be no overload situation. It comes down to judgement and experience, as well as having a bigger picture than the sector ATCO can have at any given time.
The London FMP and LAS setup might not provide the opportunity to be quite so dynamic I accept, but I know they also beaver away to reduce delays as much as they can
