The joke isn't on the Northerner or the Philipino maid.

The joke is on the posh middle class conservative bloke.

It is supposed to dipict his attitude and outlook.

Having a maid and a pet northerner and trying to mate them is a vast over exageration of his percieved outlook to others.

Nothing else.

As for little brittan, the joke is always on the other people in the sketch, not the disabled / foreign / old / gay one.

I bet you I have spelt most of this wrong.

Call me Maninibat!