The BA25 is sometimes late for a number of reasons. Usually it will be caused by the late arrival of the aircraft from LAX or a late tow from the maintenance area. Generally, it is quite a punctual flight though. I wouldn't worry.
Around 70% of the time, the BA25 hasn't got airborne within 30 minutes of its scheduled off-gate time, so to call it "quite a punctual flight" is stretching it a bit.
I can't comment on BA's towing performance, but its poor punctuality can't be attributed to late arrival of an inbound flight as the outbound BA25 has usually arrived in the morning from either LAX, JNB or HKG.