Call me an old cynic, but I would suggest that there is absolutely b*gger all chance of anything useful coming from it.
I think that the whole event has more to do with fanning the ego of the last Chief Scientific Advisor, than with a desire to achieve anything useful. It's really just a pale imitation of the similar DARPA Grand Challenge in the US.
Sorry - but it does grip my sh*t to see money being wasted on stuff like this, when there are whole areas of useful MOD research being closed down due to lack of funds.
I went to the open day last year in london. It was interesting, however my UAV concept wasn't sufficiently developed for me to take part, so I didn't sign up for the challenge.
I did contribute, in that i expressed serious concerns about how the event was structured. Whether my comments were taken on board I don't know, by I don't think my rather abrupt manner endeared me to the panel!
If it is run correctly, it could be an excellent way to generate expertise. Not only in getting the actual piece of equipment, but in developing the skills for developing suitable tech.