I've been invited to 10 Downing Street, and don't know what to expect. Can anyone give me guidance on protocol, what to expect.

granting the U.S. independence It occurred to me that if I were an American I might be annoyed by that phrasing. I'm aware that the U.S. took its independence for itself; you know what I mean.

You're not meeting Cameron, right? So there's no particular protocol. (Hell, even with Cameron there isn't, except obviously you stand if he enters the room; do this if Clegg comes in, too.) You behave as you would in a business setting. The people you meet will be very efficient and business-like, but also extremely polite and probably very pleasant. You'll find that the street is closed, and you go through security at the end. Be on time, be well attired, and don't try to impress anyone and you'll impress them. Ask them to show you the desk where George III signed the Treaty of Paris, granting the U.S. independence. Don't whip out a camera when they do; but do bring one to get a picture outside the door when you leave. Yes, if you've been invited you should expect them to pay your way, with business-class airfare on BA. Four-star hotel in downtown London, and possibly someone to meet you at Heathrow for the transfer to the hotel, though if they don't offer that I'm sure you can find your way on Heathrow Express. Have fun!

I would be shocked if 10 Downing didn't have a protocol officer. Ask your sponsor to put you in touch. They'll answer all your questions - clothing, timing, security practices, appropriate ways to interact with the audience, etc. - that's what they're there for.

No 10, both as a building and as a set of people, is smaller than you would expect. If you are meeting an official there, rather than the PM, it may help to figure out where they sit in the organisation. They may be a http://www.number10.gov.uk/news/written-ministerial-statement-special-adviser-numbers-and-costs/ - ie a political appointment. Or they may be a permanent http://en.wikipedia.org/wiki/Number_10_Policy_Unit, either one of the PM's private office or the No 10 Policy Unit. Might be worth figuring out where your contact sits in the scheme of things. You might get to be in one of the PM's bits of No 10, like the http://www.number10.gov.uk/history-and-tour/tour/the-study/, or you might be in one of the meeting rooms elsewhere in the building. Dress smartly - suit and tie for men, equivalent level of smartness for women - but beyond that don't worry about anything. When you go in, it will be through the police check at the front gate. You then wander up to the front door. As DarlingBri says, civil servants, journalists, heads of organisations and members of the public are in and out of there for meetings all day, every day.

I'm more annoyed by the concept of "Downtown London" Yeah, I thought about that and figured I should have just said "central London," but I then I don't know if that would just mean the City to people who are actually from London. I think downtown got the point across - you can expect that you don't have to take the tube for an hour to get to your meeting.

Thank you everyone for your comments. My presentation went much better than I expected. Also, I received a grand tour of the place. Still haven't come down to earth from the experience.