I would contact your insurance company as it depends how your exact policy is worded, it may or may not cover passengers in your car. It doesn't cover you or your car, just others you may injure, but passengers in your car may not be included (although passengers in other car would be). One would assume they would be, but it's best to check the small print.
For example
Aviva specifically says it covers passengers
http://www.aviva.co.u...party-fire-theft.html
but this says not
http://www.moneysuper...nce/third-party-only/
and the AA says "usually"!
It's worth getting it in writing as this will only be needed in terms of a legal situation so you need to know what is correct and that your passengers are indeed covered. There also may be small print clauses about passengers not being covered if you are benefiting from driving them, i.e. a taxi, so it's worth clarifying what is meant by benefiting - it's obvious in the case of a taxi, but could you be legally seen as benefiting if this was in court? (remember insurance companies do not want to pay out, so will know all the legal loopholes that mean they can (lawfully) avoid it).
Just get it all in writing then you can have fun on your trip.