In the case I mentioned, most probably that real estate agency lost money by dealing with Romanians and Poles in the past in a different way than it's used to lose money by dealing with local British people, that's why it put in place more complicated procedures for Romanians/Poles than it has for the locals. Yes, it is discrimination, but, again, in many cases it is based on pure material reasons, i.e. people not wanting to lose more money than they have to.
I feel like that's an open-and-shut case if "Oh, you need application form A1234-v-Romanian/Polish" is the case.
Again, that seems to be specific to that big agency, she also told me that in the past when she and her SO had found rental arrangements through smaller agencies things were a lot more straight-forward.
This doesn't get acknowledged in the West too much, that is that we (meaning countries that used to be East of the Wall) have outsourced many of our social problems to the West (which had created many of them in the first place in the '90s by ideologically imposing the Shock Doctrine therapies on us, but that's another discussion).
The thing is that this situation also affects people from those countries/societies who are not inclined to crime, such as a close friend of mine who's now having to go through lots of procedures and loops before being allowed to sign for a rental contract (she's Romanian, her SO is Polish, they've just moved from London to Manchester). All those procedures and loops are applied by the real estate agency, so not by the British State itself, I presume because the people from agency have to financially secure their back based on previous negative (from a financial pov) interactions with people from Romania and Poland (I'm also from Romania, if it matters).
Not sure what the best route going forward might be, because when you try to put yourself in each person's shoes you can understand why and how things are done in a certain way, no need to resort to "he/she is doing that because of racism/xenophobia".