Full marks to MP for the honesty on the circumstances of this infringement. Must just ask: was it in a certain club aircraft(C172S G-O..G)? That has a panel-mounted GPS, albeit with a very small map.
Also a bit surprised that your 'instructor checkout' at your flying club did not apparently give you enough familiarity with the local area to recognise important features before the heathrow tower got your attention!
I hear that White Waltham traffic may well figure on the 'evidence' paperwork at the next 'infringement prosecution' brought by the CAA following someone else's antics in the Heathrow Zone yesterday