Peter wrote:
it would really damage the Spanish economy in a lot of the sunny places, so Spain would never do that.
Don’t be so sure. History is full of political changes where the effects on economy is seen as less important.
Sure, but why would Spain bother? This is not a major issue of any kind. It would just be a loser for everybody involved. Normally, changes take place because there are some winners somewhere. Most actions have losers and winners – even if the winners keep very quiet about it (the case with most regulation, for example; the winners are the compliance business) 
Peter wrote:
If you are from Kashmir then you have no right to live anywhere in Europe unless you applied for asylum, according to the local rules – 5 or 6 years in the UK – and got it. And once you’ve got it, they can’t send you back (in general).
This isn’t right. If you apply for asylum it generally takes around a year, and is for five years, when it is reviewed. There are plenty of other ways to get the right to live in Europe, temporarily or permanently, some of which are quick (student visas) and some of which (permanent residency and naturalisation) which indeed take many years.
Peter wrote:
most refugees are “economic”
This is completely untrue. I started a charity to house refugees. The charity has now put a refugee in a bed for the night 88,000 times in two years; I have some knowledge of refugees.
The great majority are fleeing for their lives and would be killed if they went home. This includes Afghan soldiers and Iraqi interpreters who have placed their lives at risk and lost contact with their wives and children because they wanted to help the British Army. Some people are at risk from the official regimes in their countries, others from insurgent groups, like the Taliban or ISIS, others even from mafia and cartels. The bar set by the Government and courts is very high, and very few “economic” refugees get given asylum.
If you apply for asylum it generally takes around a year, and is for five years, when it is reviewed
I better go back to CZ before they find me then 
In the UK, after 5 years you can get the full right of abode + citizenship.
Review doesn’t mean return. And yes, many, sadly, are never able to go back.
As I show, I don’t think this can be disposed of with one-liners. My family applied for asylum, then after 5 years got a visit by a policeman with a briefcase who asked various questions including ones about social integration and since he was satisfied, we got the passports. No further reviews. AFAIK the process is still basically the same if your life is in danger back home, and you need evidence of that, not merely that you are a 20 year old man with a smartphone (a caricature but not an uncommon one ) who says he got away from a country where a war is taking place, having chucked away his papers along the route. The problem for any receiving country is that there are wars all over the world, always have been, though perhaps more so these days, so the requirement for the evidence is quite high. The present-day situation is very different from the ex Soviet Bloc one where (a) everybody had papers (b) virtually everybody was keen to integrate (c) nobody lied about where they came from (d) everybody came from a culture of hard work.
Peter wrote:
there are wars all over the world, always have been
The son of a friend of my mother joined the French Foreign Legion, and he said you can tell what’s going wrong in the world by the nationalities of that year’s recruits (there were a lot of Chechens at the time). Not the easiest or safest way to gain nationality though. On the upside you get 5 years pay in one go at the end, so you can buy a plane
Unfortunately, the immigration system in the UK is not “get a friendly visit from a policeman, who goes away satisfied, and gives you a passport” any more.
I have recent first hand experience of the UK immigration system (last year). It is deliberately hostile and opaque even to those we desire to come to the country (e.g. skilled workers who are high earners, and are effectively pre-integrated by coming from an Anglo-Saxon country). It is also eyewateringly expensive for the applicant. The last year’s expenses for immigration issues makes aviation look cheap – and this is for a straightforward case. The Home Office frequently lose paperwork, and in our case (because the visa is granted by the Isle of Man, not the UK, but the UKVI still processes the paperwork) it’s very difficult to get help (and the Isle of Man immigration authority is nearly as bad as the UK one – I discovered when I made a FOIA request against them that they had all the contacts they needed to be able to have asked what had happened to our paperwork, but simply chose to fob us off instead). In our case it took personal intervention by the Chief Executive of the UK Home Office to resolve the case. We were fortunate that I have the right personal contacts to do this (the Speaker of the House of Keys, who has many contacts in Westminster, is my neighbour), most people don’t have that luxury and are left hanging, without their passports and other important identity documents, for months or even years. The UKVI’s “customer service” is outsourced to a private company that seemingly can’t actually talk to the UKVI itself and despite charging you for each question and taking 21 working days to answer each question, are about as useful as a chocolate teapot – as well as often giving the wrong answers (they apparently don’t even know the process for a person from the US applying).
Fortunately we never have to deal with the UKVI or UK Home Office ever again as the next visa (and eventual ILR/citizenship) can be done in the Isle of Man – where at least we can personally visit the Immigration Office if they lose our paperwork.
The problem is faced with this is, is going to be skilled workers. We’re hiring software developers right now, and there are so few applicants from the IOM/UK we’re going to have to recruit in continental Europe. Once Brexit has been done, we won’t be able to do that any more without going through the hostile, absurdly expensive and torturous immigration process imposed by the UK. I suspect there’s an entire segment of the Isle of Man economy (the e-gaming, aka gambling industry) that will leave for Malta the day they can’t hire software developers from Europe.
The process you describe is same as I experienced c. 1985 when trying to bring over a really excellent Polish programmer and his family. After 6 months of being screwed around by the Home Office we gave up… and continued to use him as a contractor. So I don’t think “economic migration” was ever easy into the UK, in recent decades.
Peter wrote:
So I don’t think “economic migration” was ever easy into the UK, in recent decades.
It surely was for me (and all other EU people I know here), since it involved ~zero paperwork.
