The link provided by littlefish also assumes that the F passenger has either BA Gold/OneWorld Emerald or BA Silver/OneWorld Sapphire status but doesn't cover non-status PAX. Details for non-status PAX is below:

If you're flying in F you've certainly got guest rights - this page confirms this right as part of OneWorld rules. Obviously the CCR isn't part of normal OneWorld lounge access rules but as others have said, BA allow guesting to PAX not flying in F for the CCR too. This is regardless of whether you have any status yourself.

If you're flying in J and have no OneWorld status then you don't have guesting rights, it's lounge access for the PAX only.

As the link provided by littlefish shows, if you've got BA Gold/OneWorld Emerald then you've got FLounge access for you and a guest regardless of the class of service you and the guest are flying in. If you've got BA Silver/OneWorld Sapphire then you've Galleries Club access for you and a guest regardless of the class of service you and the guest are flying in.

In all of the above, the guest needs to be flying on a OneWorld operated and marketed flight. Clearly this isn't an issue in T5 as there are no non OneWorld carriers present!