Almost everything Farage says about immigration is a lie.
He encourages the idea that Britain is "swamped" by immigrants, which is untrue, that there are a large number of EU migrants on benefits, which percentage terms is also untrue, that they are a drain on the nations resources, also untrue (a strain admittedly in some areas)
He's cashing in on xenophobia and some people's pessimism (as well as the implosion of the usual party of protest).
Even that would not be a disaster, but his party is a disaster area in terms of policy. It is very unfair that they will not get the representation in Parliament their support calls for, but then the great British public voted against electoral reform so ...