No2ID has put a full-page ad in The Spectator (p.47) saying that the Home Office plans to make issuing your next passport conditional on your agreeing to be on their super-database.
Wikipedia says, "All British passports are issued in the exercise of discretion by Her Majesty's Government under the Royal Prerogative. In any event, discretion must be exercised reasonably and not on a whim, and even though there is no statute governing the issue of passports, such prerogative powers are susceptible to the normal processes of judicial review (Council of Civil Service Unions v Minister for the Civil Service  AC 374)."
I've read somewhere that there was a time when the British could travel abroad without a passport. And according to "Stiggy" on the No2ID message board, it's still legal to do so - I'd be interested to know if this is so, and how it could be done.