I am in the throws of planning my Grand Farewell Tour to Europe in the Spring.

I have studied up on the notification requirements and feel confident I can comply.  However I have a theoretical question regarding new internet-enabled devices. 

If I were to, say, buy a new phone/tablet/laptop while abroad, then it seems I would be fine with making a notification within 2 days of returning to the UK.  But what about if I were to buy it from a shop in the airside departure lounge of e.g. Gatwick airport, then leave the country that day for a few weeks ? 

Common sense would suggest that the notification clock would only start the day I arrived back in the UK, but as we are all aware common sense is none too common in the criminal justice system - I would hate to be in breach for the sake of saving a few quid !

Thoughts ?