It's turning out to be a saga as I decided to call it a birthday present to myself, bought the Airnimal specific hard case from CHWhite in Malmesbury (£125) arrived promptly, and after 1st trial pack the catch broke with a release of springs and accompanying groans. . .
Thanks for your tips; might take t'other bike and try and borrow a full sized flight case. ('Une housse' as I 'av learnt to say since I have to do part of the journey on French trains).
Thanks for tips and for clicky link - will watch that one anyway!