I stumbled across this forum post with interest, and thought that you might find the following to be of interest by reply:

I'm the owner of a new company called Slingshot Travel, which is effectively a long-range night bus service from central London to towns beyond the M25 (except that we are a coach service).

I'm in the process of marketing and building support for such a service; but if you'd like to take a look - our site is on www.slingshot.travel, and you can follow us on:

Facebook: www.facebook.com/slingshots
Twitter: www.twitter.com/slingshottravel

All going well, we're looking at launching in April / May / June this year, starting with routes going towards Milton Keynes.

Hope this is of interest!

Atull Gupta