Most of them came in the late 60's, when they were most welcome to come in and do the jobs we did not want to do. (Same goes with the south europeans before that, most of the mining towns were filled with Italians or Spanish). immigration IS a problem, a lot are still comming (and a lot die trying) comming on little boats through the Gibraltar straights, or through the turkish route.
Most of them are unemployed because all the older low wage jobs are now gone (mining, metalurgy, etc...) and the only jobs left out are fast food, trash hauling etc... we're not talking about industries of the same size as they were back then.
The same is bound to happen within the next 10 years with the easter european countries, I doubt they will ever be accepted as being part of the old europe.