ccc- I can categorically state that you are misinformed.
Liability for deportation arises after a sentence of 12 months imprisonment, or up to three periods totaling 12 months over a 5 year period. Almost all deportees start the process in detention, and very few are released during the appeal process. It is very hard to get bail. Most bail applications are refused.
Even if an immigrant has destroyed their documents, or arrived on false ones, they can be returned to their country on a one-way document.
Although it is possible to obtain false documents, there is also a document checking service that GPs and hospitals have access to.
Unless an immigrant is here for protection reasons, they cannot claim benefits until they have been granted settled status. The shortest time you can get settled status is 2 years, if you are a spouse and your partner has supported you or you have worked for those two years. For most other categories it is 5 years of showing you can support yourself financially and pay your taxes.
Is it the fault of an immigrant that they are willing to work for less money? If you believe in a free market then you believe that the market sets the level of pay. We could refuse to employ people for less, which would make UK goods more expensive, so no-one would buy them.
If people are better off on benefits, surely that is the fault of the benefit system, not immigration.