i think that we have reciprocal agreements in place with other eu countries which would entitle you (if you were in spain or germany say) to claim the equivalent of WTC or CTC or whatever provided you were eligible - earned below a certain threshhold
this can't be changed unless we pull out of the eu i reckon
non-eu migrants do not usually have legal recourse to benefits - on my work visa when i first came, i had this stamped on it, and this only changed once i received indefinite leave to remain
i don't know if the rules change if you enter the country as a spouse, or sponsored by a family member
i came knowing no one, but with a work visa for a particular job - i would not have been able to legally show up and then do some other job, or if i had lost my job, just get another, i would have had to return to my country, find a job, and my new uk employer would need to apply for a visa
in their application, they have to show that not only are there no suitable brits for the job, but no eu candidates either
i think the laws are stringent enough (wait before you choke) but i don't think that they are enforced as stringently as they could be