Illustrates the muddle of leave. They really want less immigration. Eu is just in the way of that, hence the lack of interest in economic arguments. Its single issue politics.
Technically any immigrant to the EU, illegal or otherwise should be processed at point of entry, ie Greece or Italy.
It's easier for these countries to issue local citizenship documentation than to deport... and because those initial points of entry have limited work and no welfare budget, the newly endowed arrivals move on... open borders and unrestricted movement of migrant workers within the EU means these people can legitimately come here and start claiming.
And you only have to look at the numbers of people in the Calais area waiting for a chance to get here, having bypassed/ignored France and Germany on the way (both of which have welfare systems at least as supportive as ours) to see that this is a real issue, and one that can only be tackled by being able to regulate our borders more effectively. The only reason the effects are currently not being fully felt across the country is a natural barrier commonly known as The English Channel.