Those people are already here, living somewhere, using infrastructure anyway. There are hotels which have been "repurposed" by local councils for somewhere to live for those without homes of their own. Not just immigrants awaiting processing either. We've two large hotels in our nearby town that havn't been "open" as such for several years, literally full of people just waiting to find a home to rent, when a room becomes vacant, the council puts someone else in straight away. They're already here, already using water, the roads, local healthcare, local education, etc. There's also lots of people living in unsuitable homes, i.e. on friend's sofas, families living in a single bedroom, etc., also desperately waiting for flats to come available for them to rent.
I really don't think people who are living in "steady" accommodation realise just how bad things have got. My son was looking for a flat in a new Northern city that he's moving to for his first graduate job - we'd no idea how cut-throat it would be - you can't even get a viewing unless you phone the agent, literally minutes after the home is put up on the websites to let, then you can't "negotiate" a viewing slot - you're "told" what's left and if you can't make it, tough. Those who want to proceed are listed and given to the landlord who choose which tenant they want, based on status, pets, smokers, children, occupation, income, age, how much more than asking they're willing to pay and how many months in advance they can pay! It's insane. There's no choice at all, you have to take whatever you can get a viewing for and hope that your "offer" trumps the others who want it!
We've far too many people in the country, in they're in the wrong places. There are vast swathes of semi-derelict run down areas in the run down towns (ex industrial towns and ex-seaside towns), but no one wants to live there because there aren't any jobs other than minimum wage, so those with skills/trades/professionals/qualifications have to stay in the overcrowded cities because that's where the jobs are. The empty/unlet properties in run down towns just get the dregs of society who are often "bussed in", such as newly released prisoners. Obviously such areas suffer more than their fair share of anti social behaviour and social problems, making them ever more so unattractive!
We also have major problems with holidays lets, Air BnBs etc., where local housing in tourist areas and cities is taken off the housing market due to investors who want to let them out for holidays and short breaks. Personally I think such people should be taxed to the eyeballs in both income and capital taxes as they're really damaging local housing availability and causing misery.