I have got the immigration bug worse than usual since I flew into JFK this week, where the jumble of foreigners queuing at passport control was indistinguishable from the jumble of foreigners - taxi drivers, fast-food vendors - on the other side of customs. So only two days into my summer in New York, my desk is cluttered with immigration clippings from the Times - that is, the real Times.

A taste: Tuesday's piece about the fully institutionalised, turn-a-blindeye employment of illegals in the US. Rather than do shady under-the-table cash deals, millions of illegal labourers draw a regular pay cheque. Their employers send contributions to bogus social security (think National Insurance) numbers; the government issues standard tax documents. Every year social security sends out letters declaring "no match" - meaning, the SSN is the numerical equivalent of the tooth fairy - to eight million workers. Yet letters notifying their 130,000 employers as well strongly discourage sacking any employees for their Monopolymoney social security cards.

It is technically a crime in the US to "knowingly" hire illegals. That "knowingly" loophole helps to explain why a paltry 50 or fewer people a year are convicted of hiring illegal aliens. To create plausible deniability, employers need only view documents establishing legitimacy; the documents themselves need not be legitimate. Employers are under no obligation to spot fakes, even if the forgeries are downright hilarious.

So systematised is the employment of illegals in America that the documents are rarely hilarious. Should you care to flout US immigration law - and if you don't, you're missing a trick, since everyone else does - I've read up, and here's the drill. Hang about any Wal-Mart car park. If you are not bunging bags of cut-rate chilli-and-lime Doritos the size of pillows into the boot of your SUV, you will stand out. In no time, an enterprising young Spanishspeaker will usher you into a photo booth, scoot off and return in two hours. For $110 (about £60), you will have secured a work permit (a green card), with your picture and some total stranger's fingerprints, and another card with a festival of digits pretending to be a social security number. Welcome to the United States.

It is not enough to pass a law; you have to enforce it. No enforcement, effectively, no law. Moreover, if you allow millions of people to violate your "law" they will not only become confident of their chances of getting away with it, they will rapidly come to believe that they're not getting away with anything. "Illegal" immigration to the US has segued, for the entire world, from temptation to human right. Thus millions of illegal immigrants took to America's streets in April, utterly fearless of apprehension, indignantly demanding their "rights". In an acknowledgement that unenforced laws aren't really laws at all, PC Americans now shy from the unwelcoming term "illegal immigrant", preferring the benign "undocumented worker". But chances are the worker does have documents. They're just fake.

This disappearing ink phenomenon in relation to immigration law - what immigration law? - helps to explain why the US will soon have no choice but to issue an amnesty, de facto or otherwise, to its 12 million gatecrashers, and to the millions more who follow. Britainwill have to do likewise, even with its comparatively negligible half million visitors-for-life. Sending them all back home became a logistical impossibility long ago. When you let a law slide, it evaporates. You can't shove the undocumented genie back into the bottle.

Secondly, I was bemused to read this week that Mexico has an accelerating immigration problem. Many of the South and Central Americans teeming across its border with Guatemala are heading for the US. But a fair number are staying on in Mexico, where they take "the jobs Mexicans don't want". So many Mexicans have left for more lucrative jobs in el Norte that only the Guatemalans will pick mangoes in the baking sun for a few lousy pesos.

Furthermore, foreigners ploughing into Mexico are subject to the same fierce local resentment that brought outraged Mexicans out on America's streets in April. The coordinator of the government-funded humanitarian organisation Grupo Beta declared, "This society does not see migrants as human beings, it sees them as criminals." I was startled to learn that Mexico's immigration law is far more stringent than America's, even more stringent than the harsher laws now in limbo in the US Congress, over which Mexican president Vicente Fox has been so alarmed.

This is what I mean about double standards. The very same national populations that blithely regard the US as an extension of their own backyard get very stroppy indeed when foreigners start regarding their own countries with the same presumption.

Admittedly, this is a double standard in which American mythology has been complicit. Forever talking up the "melting pot" and our proud tradition as a "nation of immigrants", US politicians can't sabre-rattle over stricter immigration policies without sounding like hypocrites. The rest of the world doesn't believe the US has the right to police its own borders; raised on all that "huddled masses yearning to be free" folderol, Americans don't either. In short, the US has been helplessly victimised by its own bullshit.

This week Lionel watched the South African film Tsotsi, "about a thug who discovers his humanity by falling in love with a baby, but which isn't - incredibly - sentimental." She also watched Brokeback Mountain: "Unexpectedly moving, and a testimony to British Airways - two movies in a row worth watching on a plane."