My dad reckons you should just cut the branch off and sit in the house
and remove the berries whilst sat comfortably... is this a good idea?

Yes. It is exactly what we do.

I've heard this advised. But I'd have hardly any branches left if I cut
out all branches with fruit on. You can get 2 years good fruiting from a
branch.

What sort of crop do you get per bush with your regime, martin? I've been
averaging between 7 to 10 lbs per bush for the last 15 years on mine.

Just curious.

We've never weighed ours. We do get far more than we can cope with.

Can't have too many blackcurrants, such a situation does not exist :-)
But I have grandchildren that love home made blackcurrant syrup. I produce
several gallons a year, in addition to the jams, jellies etc