I miss spotting at airports too, LHR would be awesome with a spotter's area plus spotters are quite useful for noticing things.
I've found the next best thing though -
Big Jet TV. They stream live at least twice a week. The first 30 mins of each broadcast are freeview on Facebook & YouTube whilst the rest of the broadcast is for "Gold" members on a closed Facebook page who pay a monthly subscription equivalent to the cost of a coffee!
These guys are awesome, very funny, and travel to other airports in the UK & Europe for their viewers. They also get some exclusive access such as airside with Cargologic (which was an awesome show).
Worth giving them a watch if you miss/can't get to airports to spot or have kids who are interested in planes!