Heavy jets VFR?
For base training details like this, an IFR flight plan is filed from departure airport to Shannon, ie EGLL-EINN and then a separate IFR flight plan for the return EINN-EGLL. No flight plans of any sort are filed for the circuit training sortie as aircraft remains within the local traffic zone. Even full stop landings for circuit training do not require a flight plan filing, simply atc Liaison. This is also the case for base training at an airfield of departure.