We presently have  references in the introduction that each state Britain and Ireland  is becoming the preferred official usage Nowadays it is the most favoured expression and that the term British Isles  should best be avoided The last quoted reference according to the Guardian newspaper So its not your mere one source  as claimed Despite these  references however bizarrely none of these well referenced facts are to be seen in the introduction of this article Canterbury Tails you ask  Why should it be in the lead  because it is now the most favoured and preferred official alternative term  Lastly on a practical standpoint say for example you were looking for a new book on the types of birdswildlife in general for the region youd be hard pressed to find any such modern books with British Isles in the title Why Because Britain and Ireland has become the preferred official usage See  Crossley ID Guide Britain and Ireland The Crossley ID Guides published   Bird Atlas  The Breeding and Wintering Birds of Britain and Ireland British Trust for Ornithology etc