Jane and I have been to the service for the past few years. We get there around 8 am and are able to get in. If the idea of waiting puts you off, it went by very quickly and the atmosphere was lovely. There are toilets and a cafe on the grounds. We bring little stools to sit on and blankets to wrap up and there are facilities to put these aside during the service. One thing that we learned was when it snowed in 2010 there were a lot of empty seats because people would not wait in that weather so if you think you might not make it in, it is worth going to see how long the line is. They will not admit more people than the chapel can hold.
If you would like to be a part of this you will need to join the line at King's College Chapel via main gate on King's Parade, the earlier (no earlier than 7:30 a.m. you get there the more likely you will get in (they say usually people who queue by 9 a.m. will get in). You won't be let in until 1:30 p.m. and the service starts at 3 p.m. This is not suitable for young children as it is recorded live.
For more information, go here.
Hope to see you there!All the Best!
American to Britain