//Is there not room for an extra 400//
No.
//(if, of course, they are genuinely displaced people, not just here for the money)//
What, displaced from Northern France, you mean?
I think I can save the taxpayer some money. Abolish the quaintly named "Border Force" (I wonder where they got that name from?). Instead, charter a cross channel ferry and just provide a free passage to anyone from Northern France who wants to get to the UK. One a day should do to start with but more may be needed as word gets round. Much easier, safer and more convenient than having to set out in a rubber boat to be "intercepted" (i.e. picked up) by "Border Force" vessels once in UK waters. A bit of funding for the free trips could be provided by UK citizens fleeing the country; they could be charged premium rates for the return trip to avoid it returning empty. The last UK citizen to leave by this method could turn off the lights and leave the country to the newcomers.