Where have you found this? Migrants not working is not true.

There's a difference between migrants and migrants. Whenever the media talks about the benefits migration brings, they purposefully mix every type of migration, from eg from Western Europe or Eastern Europe or Japan or US together, and are attempting to say importing illiterate Muslims from Africa is just as good.

Regarding migrants working, I don't know about the UK, but out of 162 877 asylum seekers Sweden received in 2015, only 4 574 are working.

They are a net economic benefit to the UK (for example).

They increase the nominal GDP of the nation -- because it's literally impossible for people arriving in a country not to generate any kind of economic activity, even in the form of taking money from someone else to feed them. How about per-capita GDP though? How about other metrics, like crime?

Also the crime statistic is skewed as most migrants are young men and young men commit A LOT more crime than most people - so it’s not migrants committing crime but young men

Even when adjusted to income, sex and sociological status, migrants still commit disproportionally more crime. Especially from certain countries like Algeria and Morocco, where the difference can be an an order of magnitude greater compared to other immigrant countries. The propaganda in the media is pretty effective at keeping people in the dark about these things. Many liberals in the US believe that the justice system disproportionally targets and arrests black people, but have no idea that the reason is that black people in the US do commit a disproportionally massive amount of crime.