The biggest block to the successful online use of digital identity in the UK could be MPs and lawyers and their outdated notions of identity, according to David Birch, a director of technology advisers Consult Hyperion.

Speaking ahead of the 4th annual Digital Identity Forum in London next week, he says the notion of a single over-arching ID card is both unnecessary and outdated.

"The problem is that lawyers and MPs have no concept of ID except in 1984 mode," he adds. "There's no feeling for the spectrum of technical possibilities. MPs don't know anything about keys and so on, they just think it's like a passport - either it's Big Brother or nothing. An ID card is a very good way of helping people do things, but a very bad way of stopping them doing things they want to do - there's an asymmetry about it."

He points out that most of us could have verified IDs with several different trusted organisations, any of which could be used for a variety of purposes. For example, why should we need a separate ID to access the Inland Revenue website if we already have an ID issued by a bank?

Birch says that, for online use, it is essential to add the notion of having multiple partitioned identities, just as many people already have multiple credit cards or different email addresses for different purposes.

These multiple identities are called 'pseudonyms' or in the language of the European Commission Directive on Digital Signatures, 'indirect identities'. The crucial point about them is that someone (such as your bank) knows who you are but that counter parties in online worlds do not.

"We need a more sophisticated concept of identity," he says. "You don't need to know who someone is to make valid transactions, in fact there are good reasons not to know. For example, a 'stealth card' with no name on is safer if you lose it - having your name on your card is a historical artefact. All that a digital ID really has to do is verify that the person presenting the ID is indeed its owner and that they are authorised to do whatever it is they are asking to do.

"A single ID is not enough to support all the rich mix of things you need to do," Birch says. "The difference is that kids partition their identity unconsciously, while older people partition their identity consciously - different addresses for friends and the bank, say."