That's only because things aren't serious yet. If there were dedicated political will the channel could be handily sealed off, and it's great that we aren't in such a dire place yet but were it to arise those boats would never make it.

The argument, rarely said explicitly except by talk radio hosts, is that the navy will be deployed to either mass murder them directly or to hole their boats and leave them to drown. As happens in the Mediterranean.

(This is obviously a crime, so special legislation will be enacted to let the state murder undesirables)

At the moment, the French navy shadows them into british waters, and then the RNLI provides a taxi to shore for them. They then manage to remain in the UK indefinitely.

And the people smugglers make about £5k per person for the migrants.