Alan Johnson has been visiting Manchester to promote the - now-volutary - ID card scheme.The scheme is being trialled in our region. So far, the home office says, 3,500 people have applied for the £30 cards.The cards are now being sold, in the home secretary's words, as 'a convenient piece of plastic' that will allow people to prove their identity without having to provide 'six months of bank statements or crumpled gas bills'.Mr Johnson added: "I don't think it would be right to insist that they