I wonder whether this is a new and permanent trend, or whether these are slotting sitting at LHR, awaiting more lucrative destinations with high business or connecting traffic.

Perhaps BA are also waiting for the LGW move to occur and bed down before loading in lots of extra leisure flights.

Summer weekend leisure flights make sense from LCY, where the slots have little alternative use; but it harder to make that case for LHR slots. One consequence is a far higher CE fare than would be the case ex-LGW.