Sean Dell.... It shouldn't involve multiple heading changes and more work "down the line". Getting a jet through a clockwork mouse is a routine ATC move that probably occurs hundreds of times a day in UK airspace. Sure, if the opportunity arises then put the first one off first... but it's no big deal for ATC.
Yonks ago at Heathrow and aircraft called to pushback and was cleared to do so. Seconds later another aircraft called from stand B19 to push and he had an earlier slot time so the first aircraft was told to cancel push and wait until the other one had gone. Pilot said: "What am I to say to that?" ATC: "Wish I was on B19?"