Thanks Arthur. Yes they've said: The following do not require a visa to enter Gibraltar
persons holding EU issued family permits, UK Residence Permits valid for a period of 12 months or more, UK Biometric Residence permits or a UK multiple entry visa valid for 6 months or more.
I'd guessed that was the case but I wanted to be belts and braces. All it needs is one little anomaly and we'd be back on the plane.