Should be fine; I've done it myself.

Only other annoyance may come if for any reason your flight is cancelled at LHR and there's not another out, as you will have to exit the airport via the border. They're fine about it, but you have to go into the queue with people from countries which aren't e-gate compatible. Which can also be fine, but can also be a long queue. Very small chance, but I've also done this myself