London-here we come!

We are currently driving from Palm Desert to LAX to catch our 4pm direct flight to London Heathrow. I’m so excited but already exhausted. We will arrive Tuesday at 10:30 am and start exploring. I have to admit i put a lot of planned into this trip so everything goes smoothly. Got our tickets to Buckingham palace, Tower of London, Churchill War rooms and of course a half day bus tour. I decided as against the London pass and just purchased tickets directly from the sites. I think it saved me money and guaranteed we would skip the lines. I heard the Queen will be expecting us for afternoon tea. Any suggestions where to have tea?