If you have an adventurous streak that has to be addressed, there's a London to Mongolia car rally you could run

http://www.theadventurists.com/ bring you the Mongol Rally

I love that they limit the cars to .. ..

"The Vehicle Rule:
You can only use a car with an engine of less than 1 litre that is generally considered to be crap. Motorbikes are limited to under 125cc, ideally scooters. You should be careful not to limit your own fun though. The Mongol Rally is not about making sure you reach Mongolia but the fun you have trying. If you get there with no hiccups you won't have any fun. Exceptions to this rule may be considered for vehicles of notable unusualness with high comedy value. "

And a rule about raising money for a charity (cool), and the rule that you are on your own.

Other than these you are free to sneak, bribe, cheat, connive and generally out-wit the world to get yourselves to Ulaanbaatar. In fact you will probably have to. If you get to the end of the race without some good stories to tell, then the Mongol Rally has failed in its mission. Which it won't.