The Royal Garden Party, regardless of location, is a great occasion and well done for scoring a ticket. The wife and I went a couple of years ago to Buck House and will be one of those things we will be talking about for years to come. We decided to make a couple of days of it with a day's leave either side of it. The RGP itself is classed as duty so there's no need to put leave in, however travel and subsistence can't be claimed for. We stayed in a hotel about 150 yards or so from Kensington Palace and the day we went it was around 32 degrees so we walked through the gardens and Hyde Park before getting the underpass near the Lanesborough Hotel. There are queues all around the walls of the gardens but as soon as we headed towards a queue, an Aussie Flt Lt who was in the process of showing his invite to the police saw us and shouted over "come in with us mate" so we got in more or less straight away - none of the public seemed to mind this either, which we though was really good.
As soon as we got through the gate, you enter HM's back garden which even in a prolonged dry period of hot sunshine, still looked absolutely magnificent. All of the guests more or less have the run of the place and provided you don't wreck anything, take anythng, etc, no-one minds at all and it's a real privilege to see areas that no-one else ever gets to see. At the top of the garden by the rear of the house there are two tea tents - the one that you use and the one for the royals and their invited guests (diplomats, etc). The amount and quality of food and drink available to you is second to none and you can stuff your face as much as want - all of the usual afternoon tea fare such as sandwiches, cakes, stickies, etc. The tea that is served is a special blend from Fortnum and Mason and is to die for (I love my brew and it really is something special). It's not available anywhere else other than Buck House which is a real shame as it really is lovely stuff. It is reckoned that the royals cost everyone in this country 67p per year and I certainly had my 67p's worth of scran, my wife's and all of our friends and colleagues that we had probably met in our lifetimes!
At 1600 on the nail, the royals congregate at the top of the steps and the anthem is played. Depending on the day, there will be a selection of the family out to have tea. We were really lucky in that most of the big guns were there - Charles and Camilla, Anne, Sophie and Edward as well as the Queen and Philip. Officially, the flunkies in their top hats and tails walk around the grounds talking to people and ascertaining who has an interesting story to share with the Queen - most of the people there are ordinary members of the public who have raised thousands for charity or given years in public service (we got talking to an old man and his wife and he'd been a lollipop man in his village for 60 years) and are recommended to be invited by their Lord Lieutenant - however protocol soon goes out of the window. We were in an unofficial receiving line for Charles and Camilla who spent ages working their way down it as they stopped and spoke to EVERYBODY and are indeed a very pleasant pair of people. You turn around and you see Philip stood behind you, talking to his mates. It really is a surreal experience! They soon head over to their tea tent for their brews and sticky buns. As I said, you have the run of the gardens and is very nice to be able walk around and take in the surroundings. As I said earlier, we had 32 degrees with hot sunshine so there's even ice cream served which was a nice touch.
At 1800, they head back to the top of the stops and the anthem is again played signalling the end of the party. You leave through the house, again seeing things the public don't get to see. As you head to the front, the tourists go ballistic and the wife and I were asked to pose for photos for several yanks and Japanese people!
My advice is definitely wear your No 1s, more than anything to facilitate ease of entry. There's no bullsh1t at the party so no saluting, etc, despite there being lots of officers from the Household Div, etc who believe in that kind of thing. It's a very relaxed occasion. But most of all, enjoy it - it really is a once-in-a-lifetime opportunity and provided the weather stays nice it's a pleasant, but surreal, way to spend a summer afternoon.