Let me know if you want to park in my driveway in Twickenham. You can take the train from Whitton (5 mins walk from my house) to Vauxhaul (direct) and then a 10 minute walk to the Embassy.
My daughter is at the Embassy this morning to renew her expired passport, 8 am appointment. Even though she's 18, they make her show up in person for the first adult passport. Of course, she prepared nothing in advance so she's going to rock up without any pictures or prepaid mail envelope. There's a photo booth there and supposedly a post office nearby that's open before 8 so maybe she can work it out.
Keep your eye out for the cool overhead glass bottom swimming pool that goes from one building to the next. It's right next to the entrance.