The official response on BA Intranet:
Question
Can I use the Airport Lounges?
Answer
Employees and their eligible nominees may not make use of airport lounges when travelling on personal travel concessions. This is irrespective of their cabin eligibility code and the type of concession being used. This includes premium standby concessions.
Only in the following circumstances may a lounge be used:
1) Where an employee is travelling in the company of a British Airways Premier, Gold or Silver card holder, themselves travelling on either a full commercial or rebate travel ticket, access may be granted to the Terraces/Galleries Lounge only as a guest of the card holder, subject to lounge capacity. This does not apply to oneworld Sapphire or Emerald card holders.
2) Where the employee is a British Airways Premier, Gold or Silver card holder access may be granted to the Terraces/Galleries Lounge only to the employee plus one guest who may also be travelling on a rebate ticket, subject to lounge capacity. This does not apply to oneworld Sapphire or Emerald card holders.
3) Employees travelling on duty and who have First Class cabin eligibility may use the Terraces/Galleries Lounge only, subject to Lounge capacity. Employees holding a Diners Card may be eligible to use 'Diners' lounges.
So, from that, I would take it that you have to hold status to guest someone into the lounge. Do you?