just an addendum here. 'Yes' only applies to the LHR lounge.

The PMI lounge is a contract lounge, where the policy is :

Diamond Club Gold card members - no guest
Diamond Club Silver card members - no guest
bmi Business Class passengers - plus 1 guest
Economy Flexible shorthaul only and YBMI/BM tickets - no guest
Star Alliance Gold card holders - no guest
Star Alliance 1st passengers - no guest
Star Alliance Business Class passengers - no guest

and since BD don't do Business Class on the PMI route anymore, the only "+1 guest" option is now off the menu.