The workaround:
(1) Go to www.irctc.co.in and click 'Signup' under the login button to register for an account. In the mobile phone field, simply make a 10-digit number up. You may also have to knock the last letter off your UK postcode to get it accepted, or simply use that old favourite '123456'. But they won't phone you or send anything to you, so none of this matters!
(2) Then email their customer care department (care@irctc.co.in) with a scanned copy of your passport and your user name. They will activate your registration without an Indian mobile number.
(3) You can now buy tickets at www.irctc.co.in, as explained here. When it comes to payment, be sure to select 'Visa/MasterCard with Citibank', as this should accept overseas cards. The Axis gateway does not accept overseas cards.
(4) In theory, once you have an IRCTC account you can now buy tickets at www.cleartrip.com using a ridiculously complex combination of your activated IRCTC account details and your Cleatrip.com account details, but I have not managed to get Cleartrip to work this way. So use this workaround to get an activated IRCTC.co.in account, and book at irctc.co.in as explained here, using the Citibank payment option at the payment stage.
(5) If all else fails, book Indian train travel in advance by buying a ½ day, 1 day or longer IndRail pass from UK agency www.indiarail.co.uk. See the IndRail pass info here.
La marche à suivre a été mise à jour aujourd'hui et est normalement adaptée aux cartes étrangères... J'essaierai quand mon compte sera ENFIN accessible
(le pire dans tout ça... c'est que j'ai même pas besoin d'acheter un billet de train )
"Au moins une fois par an, ou aussi souvent que possible, allez quelque part où vous n’êtes jamais allé auparavant." Dalai Lama