Last Sunday at Heathrow T3 lounge around 11am F side was completely full. Much more room on the J side. I actually prefer the J side to the F side in the morning, the breakfast buffet is better for me than the a la carte - there is no staff member to judge my sausage eating shame before the flight. Only a third of the lounge on the F side left when the flight was called, rest must have been OWE on other flights that day.

Sadly no chance of a DM/F only lounge in LHR though