Basically, there's no need to rush/stress/panic, but do try and find
out how they made it in and then block their entry so they don't become
an annual little 'visitor'.

Seri

P.S. don't fall for the misconception that wasps are bad, they're
actually quite nice little buggers (unless they sting you).

Thanks Seri,

I don't believe they are bad; I don't want to have to live with them in the
house with my family and pets.
All of us have suffered stings over the last few years, nothing disastrous
but painful at the time.
This isn't a knee-jerk reaction, believe me.
In my OP I said that the roof has sarking and not felt. This means that
there will be small spaces under most rooftiles that might allow ingress. A
rough calculation gives 130,000 roof tiles. That's a lot of small spaces.
Probably time to consider re-roofing the whole lot but where to find
someone to cope with this lot. Listed buildings, tythe barns etc.

Many thanks for your advice

Nick.