HOWEVER well-intentioned they start out, invented criteria for assessing Britishness invariably descend into silliness bordering on the downright bizarre. You need only consider one of the many Home Office-inspired online citizenship tests to see that.

Passing it will require you to know, among other things, how many days a year schools must be open (190), and what proportion of the population has tried illegal drugs (one third). That being in possession of these two random facts should qualify you for (and not being debar you from) British status is clearly absurd.

Try thinking of something better, however, and you soon realise how complex it is to categorise Britishness with any degree of accuracy.

But although Britishness is hard to define, it is often easy to recognise. And, grand abstractions aside (think tolerance, humour, fair-mindedness, courage in adversity, that sort of thing), it is far more likely to involve everyday things such as mustard and biscuits. Let me explain.

To go into a shop and ask for a jar of Colman's, or a packet of Rich Tea, and be met with blank incomprehension, is slightly disorientating. The words are simple, but the message that they are intended to convey is not getting through. To ask where the piccalilli is, and to be directed to the pickles, is similarly to be faced with a lack of those shared references that oil the wheels of social cohesion.

If this month's Home Office report into the downside of mass immigration is to be believed, such barriers to easy communication can only increase. True, the inability to locate a mustard-based condiment delicious with a plate of cold cuts is a minor irritant. Other experiences could prove to be less so.

The Lincolnshire market town of Boston, for example, has the largest concentration of East European migrants in the country. Many locally born residents, hearing the voices of Poles, Latvians, Lithuanians, Russians, or Romanians on their High Street, admit to feeling like strangers in their own town.

But when one local woman with family connections going back many generations dared to draw attention to this uncomfortable fact on Radio 4's Question Time earlier this year, she was loftily dismissed by one of the panellists.

Nor are the problems confined to Boston. The report revealed that half of the country's population now lives in a town or city affected by demonstrably high levels of immigration.

Schools struggle valiantly to teach geography or maths or history, but have to factor in TEFL in order to do so, while English-speaking children twiddle their thumbs. Actually, they often make pretty good progress, thanks to the heroic efforts of teachers. But that is another story.

Pressure on housing and social-services departments, hospitals, the emergency services, and the courts, grows, as already hard-pressed institutions groan under the weight of increased and accelerating demand.

The slow absorption of foreign cultures into our shared way of life has been beneficial and enriching. But to expect large numbers to be integrated overnight (or even over a decade) is to have unrealistic expectations of people's capacity to accept change.

Indeed, as ten per cent of Boston's 65,000- strong population now comes from Eastern Europe, we may be entitled to ask who should integrate with whom.

The benefits that hard-working immigrants have brought this country in recent times are real and considerable, and we rightly celebrate their contribution to British society. But merely to question the speed with which this transformation is happening should not incur the charge of being a racist.

The issue, to repeat, is not immigrants: it is immigration. The problem is not people: it is numbers, and management of those numbers. And it will take more than the piccalilli test to get the balance right.

Trevor Barnes reports for the Sunday programme and other BBC Religion and Ethics broadcasts.