And if you do see two legs available, ring up to book it, don't snap up the PHL tickets and then separately handle the WAW service, unless you are actually stopping off in London anyway. Note that WAW is Terminal 3 currently, which has advantages in terms of lounges but disadvantages if you arrive into T5 on BA metal (for the companion ticket). I'm told this route is under review and may go to T5 (no dates, just rumour territory).

CW looks quite good from PHL to LHR, WTP is problematic on Thursdays and Fridays leaving PHL, and around the weekends from LHR. BWI is your other option, not that it has much WTP either.