Believe it or not the Mongol Rally is actually pretty dangerous. Lots of very bad things can happen to people on the roads between the UK and Ulan-Ude. Some of these bad things can be expensive, some of these bad things require medical evacuation by helicopter to a country with medical facilities which can cost millions. To prevent these bad things from flinging you into a paupers jail for the rest of your life, we recommend decent travel insurance. It might also be important as some good cover will mean you're not out of pocket if the team's rally plans cave in before the launch and the refund period has expired.
The folks at Campbell Irvine have been insuring ralliers for a decade now so they know the general score. They understand the risks on our adventures and are comfortable offering cover to any teams based in the EU. They are not the only insurer available but remember that it is your responsibility to ensure that the company you use understands what the Rally entails and the risks involved. Many insurers may reject your application on the basis that their policies cannot cover you for the risks involved in doing something like the Mongol Rally - so you may need to research your options extensively and persistently.
Campbell Irvine are a separate organisation, so if you are interested in what they have to offer or have any questions about the cover they offer you need to contact them directly. Telephone +44(0) 20 7937 6981. Email firstname.lastname@example.org.