I will be in J on SQ322 SIN-LHR arriving on Dec 31 at 5:25 am and then connecting to AC869 LHR-YYZ (also in J) leaving at 9:00 am on the same morning. Since both carriers operate out of T3, I'm assuming that I won't have to clear immigration (Probably the only saving grace of this connection). Is that correct? All I have to do is walk from my arriving gate to my departure gate? Which lounge should I utilize based on your recommendations: SQ's, UA's or the *A Gold? 5:25 am is pretty darn early, is Heathrow really dead during that time of day?