Originally Posted by
WHBM
If you are not staying in the UK just write the words "In Transit" in the accommodation detail. You can put something like "departing SA123 22.30 01/04/2007" to clarify. There are thousands of transit passengers through Heathrow each day. And it's quite OK to go out into the main terminal, or up to London for a few hours, while in transit.
This will do it, and have your onward tickets handy in case they ask to see them. I've never been asked, but I've had reports of people who have.