Mathew Paris (he did say this was OK) rather hits the nail on the head here:
Far less persuasive are the so-called concessions that the Home Secretary, Jacqui Smith, is advertising. They are a travesty of the spirit of our unwritten constitution. Giving the House of Commons an administrative function in the arrest, detention and possible charge of individual suspects drives a coach and horses through the theory that Parliament legislates for the generality, and the executive and the judiciary apply legislation in the particular.
The Commons has no business – nor expertise, nor information – making determinations as to how the law should be applied in individual cases: the idea\’s a contemptible piece of careless ad-hoc-ery. Anyway, what happens when Parliament isn\’t sitting?