Actually, opposition to immigration is perfectly consistent with libertarianism. Hans Hermann Hoppe is an "anarcho capitalist" philosopher who regards open-borders immigration as "forced integration" rather than free association, as he explains in this article - http://www.lewrockwell.com/orig/hermann-hoppe1.ht....

Still, you are right that UKIP is not properly libertarian. But when most people hear the word, it's usually taken to vaguely mean "the government should do less" rather than as referring to any sort of specific philosophical principles. So I think it's a good description.

Unfortunately, number 2 on the Lib Dem GLA list is Stephen Knight, and there is not a chance he would choose a coalition with the Tories over Labour - he is on the extreme left of the party, and openly opposes the coalition government. Caroline Pidgeon (first on the Lib Dem GLA list) is also closer to Labour than the Conservatives. So unfortunately, this post is little more than wishful thinking.