(Was the gig in Ireland, or does that make any difference?)
"...a woman approached me and said I was not a bad singer for an Englishman ".
Your riposte should have been "I'm not bad between the sheets either - fancy getting your kit off?".

If it was in Ireland, let it drop, there's no mileage in this for an English singer, who
(I understand ) does a fair amount of bookings over there.
I can't believe there was any harm meant, it's just backhanded compliment as someone I think has already said.