If "THEY" wanted to get into the UK then Calais is the LAST place "they" would try.
Did you know the coastline of the UK including principle islands is 19,491 miles long, all of it unguarded, other than specific crossing points, in particular CALAIS? These terrorist organisations have shit loads of money. If they wanted to get someone in, then buying a boat and crewing it, and landing it somewhere undetected on the 19,000+ miles of unprotected coastline would be a piece of piss.