Immigrants? Britain is plain full of them. Think of the House of Windsor, a hotch-potch of German and Greek ancestry with assorted other European bloodlines stirred into the pot. Think of such prominent Tories as Malcolm Rifkind and Michael Howard whose families successfully sought refuge from persecution before knitting themselves into the fabric of British life. Think of Charan Gill, whose Punjabi grandpa told the nine-year-old immigrant he would be judged on the level of his ambition. The multi-millionaire is emblematic of many Scots-Asian success stories.

Think of the more recent wave of young Poles, impressing all and sundry with their attitude and work rate and cheerfully signing up to the European ideal of free movement of labour; a sort of longer-term variation on the gap year. But whatever else, think of the issue as about so much more than the raw statistics over which the politicians got down and dirty yesterday.

Is immigration an unmixed blessing? Of course not. The information gaps have left many councils in England struggling to service the educational and health demands of a population not yet conversant with the language. Neither is it sustainable to think of immigrants arriving on these shores as a tidy homogenous group, even within the same cultural mix. Among those Londoners horrified at young Jamaicans topping the list for gun-toting gang crime are the long-settled, God-fearing, post-war Caribbean families whose lifestyle could hardly be more different. There are problems, too, with the fact that some arrivals from places such as Somalia or Albania can demonstrate simultaneously real danger if they were to be repatriated, and an unhealthy involvement in criminal activity.

That's always going to be a tough call. And, as a recent Channel 4 documentary pointed out, certain nationalities traditionally transplant better than others, even when originating from adjoining countries. In short, immigration is a complex business which, with the right infrastructure, can confer many benefits, not least in a country such as Scotland which, until recently, suffered serial net population loss. But it can also create many tensions, particularly in the currently febrile atmosphere of those British cities where mutual suspicion and ignorance between indigenous and incoming tribes has created a de facto apartheid, as we witnessed during the riots in the north of England not so many summers ago. The 7/7 London bombers being born- and-bred British Asians reopened some of these multicultural wounds.

David Cameron, dipping a cautious toe in the waters of a debate that contributed to his party once being called "nasty" by its own chair, began his speech by talking about the benefits of immigration and the need for a grown-up conversation about it. Amen to that. What will not make that conversation adult are snap judgments or oven-ready policies from any party pandering to the knee-jerk prejudice of the latest focus-group polling. We need to deal in facts, not slogans. Gordon Brown's "British jobs for British workers" may be meaningless rhetoric, but it's manna from heaven for right-wing bovver boys, and uncomfortably close to their Britain for the British diatribe. Always supposing you manage to define British. Neither is Mr Cameron's suggestion of capping numbers arbitrarily the logical way forward. What happens if some kind of human catastrophe occurs after the quota is agreed for the year?

A civilised country, which Scotland surely aspires to be, should continue to offer asylum to those who need it, and arbitrate on their application for refugee status as swiftly as possible. It should not, under any circumstances, house pending families in former prison blocks. It should continue with, and further nourish, the previous administration's Fresh Talent initiative to allow non-EU graduates to employ their skills and experience here. Recently, a raft of very bright immigrant teenagers was finally able to access higher education on the same basis as their fellow students, which was no more than enlightened self-interest. It's never been clear to me why anyone should get hot under the collar about so called "economic" migrants; scratch the surface of any Caledonian society worldwide and you'll find it set up and run by just such citizens of their adopted country. And when expat Scots celebrate their roots, it's regarded as perfectly natural rather than a refusal to assimilate.

You will not find the current batch of London-based, foreign-registered billionaire businessmen cited as economic migrants, despite their extremely favourable arrangement with the British Exchequer. If you're sufficiently wealthy, none of the anxieties or normal rules of conduct applies. Indefinite leave to remain? Just sign here, sir and could we humbly suggest your chauffeur doesn't double-park the Roller?