Transport for London has announced the sale of its 10 millionth Oyster card. Its what? The future, for better or worse.

For the vast majority who don't live in the throbbing metropolis (London, that is, not the one in Superman), the Oyster card is a futuristic electronic swipe-card by means of which smog-bound Londoners pay for transport on tubes and buses.

Credit can be purchased in a variety of formats and via stations, shops, the web and mobile phones. If your card is nicked or lost you can reclaim your account's moolah, and Oyster means that up to 40 passengers a minute can pass through underground payment gates, which is nearly three times the number of paper tickets that can be validated in that time. That makes me less late for work.

In the not-too-distant future train services should also be purchasable, and (according to my exhaustive tests) Oyster goes through the washing machine without breaking. It's a cracker.

Indeed, mayor Red Ken says that Oyster is "bringing huge time savings to passengers and the transport system". And from my experience he has a point. But some would say there is a more sinister side to all of this, and it's becoming increasingly relevant to us all. You see, for perfectly legitimate reasons, Oyster records the pass-holder's journeys, and you have to register to have one. And while the Bishop of Southwark may be pleased about this information gathering, not everyone should be.

The world and his wife (and their scabby dog on a string) throw up their arms in rage and despair at the merest suggestion of a government-backed credit-card-style ID card, but they're perfectly happy to carry the Oyster card. (To recap, the Oyster card is a local government agency-backed credit-card-style swipe card). And as our lives, data and finances increasingly move online, Oyster nets a rich harvest of information.

Personally I have no problem with the mayor of London knowing how regularly I fall into a drunken sleep on the District Line and wake up in Barking (crazy name, crazy place). I suppose the information could be used for nefarious reasons, but the convenience of being able to pay for a month or a year's worth of travel without actually doing any travelling (or joining a queue) means I can make my peace with it. And Ken probably likes to know I get home okay.

Similarly, I can accept that my Gmail account means that Google owns me. There's not a lot it can't know about me, my buying habits and the amount of time at work I spend on personal email, and at some stage it's gonna work out how to exploit that information. And, while Google might sell me some cool stuff and have great PR, it is a money-making organisation, unlike TFL or, say, Her Majesty's Government.

The fact is that the only absolute way to protect personal data is to do nothing, go nowhere and never, ever go online. I'm not all that comfortable with the idea of successive governments knowing everything about me, but I'm resigned to the fact that it's gonna happen. And it will be convenience rather than spurious terror threats that will drive it.