One unexpected benefit of the Home Office's obsession with 'counting them all in, counting them all out' is that in the event of, say, a flu pandemic it would be simple to grab a list of all the passengers on an affected incoming flight, and check them out for infection. But no, not exactly - that's not quite how it appears to work.

Although the e-Borders system was intended to count 95 per cent of all passengers to and from the UK by 2010, and is scheduled to be covering 100 million passengers a year by June, the UK Border Agency received no passenger data for the flight that brought two known swine flu victims from Mexico to the UK on 21st April. And the public prints are reporting that the hunt is on for "five sweating and coughing men on the flight".

So how does that work? Didn't we count them in?

There are several strands to e-Borders, the most important from the point of view of counting people in and out being the passport check. But although this can be used to log movements in and out of the country, it clearly doesn't associate a particular passenger with a particular flight. Alongside this, however, the Home Office is beginning to require that airlines, ferry companies and rail operators submit passenger lists prior to the passengers' arrival.

According to recent Home Office documentation, test systems have logged 50 million movements and checked them against watchlists before the passengers arrived in the UK, resulting in 1,700 arrests. These systems undoubtedly do not yet apply to all passenger movements, or even all air passenger movements, but because of the 'apples and pears' nature of the data the Home Office publishes, it's difficult to assess the extent of the system currently in place.

According to a Home Office spokeswoman the collection of PNR (Passenger Name Record) data is being rolled out by airline, rather than geographically. But for "operation reasons" the Home Office declines to says which airlines are covered and which are not.

But it seems reasonable to assume, even if you're not a terrorist or illegal immigrant, that the airlines that are currently contributing data are the bigger players with more sophisticated data handling systems, while the package holiday operators and charter flights are at the back of the queue for inclusion, and likely to remain there for some year to come. Note that the '95 per cent by 2010' promise covers logging at the border as well, so could probably be claimed to have been achieved with no contribution from PNR data at all.

But note also that this particular target was tweaked in a footnote, here, so that UKBA is now only committed to count in and out 99 per cent of all foreign (non-EEA) passengers by 2010. That switch points to a greater emphasis on biometric visas for non-EEA passengers, and to passport rather than PNR data checks.

And while the Home Office is attempting to paint the collection of airline passenger data as a success (that 1,700 arrest figure), at the same time Jacqui Smith is telling Lord Carlile that it's not really delivering.

That, together with the difficulties of getting every last low-cost charter's data into the system, could easily lob the whole thing into the middle distance, so maybe the giant data crunching machine won't be in a position to make a contribution to controlling the next pandemic, either.

The passenger list from First Choice Flight 578 from Cancun was reportedly deleted 24 hours after the flight's arrival, although the Health Protection Agency is also reported to have asked subsequently for a passenger list. At time of writing First Choice had not responded to The Register's calls. Like you, we find it difficult to credit that ten days after the event, nobody seems to have had the nous to run a list down. ®