Nope, not a load of ****. It stands to reason that if I go out and bonk someone over the head here in Germany and they go to the police and say it was 'someone with an English accent' then they no exactly where to look.
One of the biggest problems is that Britain has no effective registration system - when I move house here I have to register it with the local authorities and I get written certification that I have done so (Anmeldebestätigung) - without this I cannot open a bank account or a health insurance, and cannot get a job anywhere. All money for all work, even social security payments, are paid here by direct bank transfer. This means that Germany knows at any given point in time exactly how many people of a certain nationality are in the country and, where they are. It also works as a filtering process. Unfortunately all you have in the UK. are estimates - and Ukip estimates are different to other estimates, and cannot, unfortunately, be readily contradicted. The problem with Britain is that it is too easy to get lost there - people go there thinking it is the easiest country to get semi legal, cash in hand jobs - which it is. All the means are there to control undesirable immigration without having to leave the EU to do it.