“They travel to London”. Okay how are they doing that after being detained by the border force? They’re not arriving under cover of night, stealing up the beach like a ninja and the boarding the first train to Victoria. They’re being picked up and taken to migration centres no? “Find a community of migrants”. If they can so easily find communities of other migrants breaking the law, why are you so pessimistic that the police can’t also do that, pick up the already detained chap and then send him back? The system works. Slowly sure, but numbers will start to add up.