Some debates on immigraion have been had but the have generally revolved around numbers, how one monitors numbers coming in and how one might control immigration (not only practically but also on what basis).
I think the debate that needs to be had is about the impact of immigration on this country's infrastructure.
A few groups (from the rozzers to charities) have attempted to begin a discussion about the repercussions of immigration in this regard in particular but whenever that has reached a 'national' level of debate, i.e. them darn politicians, the debate has returned mostly to numbers, quotas, points systems and the like.
I don't think immigration has been neglected but the next steps down the line and beyond have been.
Would that any politicians had the balls to look more than skin deep on a subject.
Again, I disagree, the debate on infrastructure is one which has been had. The area which IMO has been neglected and no real solution put forward for is that of integration and other social factors.