Originally Posted by wideman
They may also need a visa. (I dunno about UK subjects; US citizens do need one.) If they do need a visa, they can get one at the airport (US$50), but they can also get the visa from the Kenyan embassy or consulate before they leave the UK (which would make the airport bit a lot simpler).
Pretty sure they'll need one if they're going for more than 30 days; if it's less than 30 days and they're UK subjects, they may not, for largely historical reasons.
Oh, and I believe the cost is the same whether you get it at the airport or in advance.
My passport has quite a lot of Kenya stamps from last November, and I'm hoping to double the quantity this November.