It really does depend on the agent. If you are flying from LHR T4, always go to the lounge near gate 1, rather than the one near gate 10. They are more lax there with respect to the rules.

One time I was travelling out of YVR on BA. I was QF WP at the time, and I was travelling with a QF Gold. Would they allow us to take three guests into the lounge - no way !