I am looking for a definitive answer on this for Gold card holders.

BA seems to have changed the rules - the printed rules used to give a clear indication of what was allowed.

i.e. when you could use a BA lounge and whether you were allowed a guest when flying on a non-ow codeshare.

now the printed rules just refer you to ba.com. Here there is no mention of what happens whenyou have a BA numbers flight but on non-ow metal.

A simple example would be flying LHR-DUB on EI with a BA flight number - I have always been able to bring a guest with me into the terrace, but a silver friend has been denied access and told to use the EI lounge (ugh). What are the rules?