Where are you flying into EWR from? You can try to go standby on an earlier flight if you are on the last flight to EWR, and if CO perceives the London flight to be jeopardized by a weather threat, they might throw you on the night flight when you arrive in EWR. If that is full, you might be able to talk them into jumping the Paris, Brussels, Amsterdam, Frankfurt, or Cologne etc flight, and then jump a cheapie the next morning to London when you arrive. Just stay on the attack and make it happen, don't hope it happens. Have your alternatives ready.