Reminds me of my last night in London! At 9:30 pm discovered the vermin, so thought I'd just go on to Heathrow as I was leaving in the morning. Ended up at the wrong terminal! Finally, the right one, but not really supposed to be staying in the terminal overnight. Cafe Nero to the rescue! Lattes and biscuits and a couch helped. OH! Did I mention I'd taken a water pill at 9:15 p.m.?! Fortunately the RR was close to Cafe Nero!
Heard there is a spray the is TSA approved that repels the critters. Best of luck on your trip.