I'm open to correction but as I understand it,if you are inbound to T5 and connecting to either UK domestic BA or to club Europe on the same pnr,then you have access to the CR and ergo so does someone you guest in.

The best person to ask here is probably Dilly or theres another BA staff member here who has more direct involvement in who should have access to the CR.
Their name escapes me but they will be along hopefully