The so-called 'C-17 / C-130J' solution is not politically acceptable to certain A400M customers. Neither is the C-27J an adequate alternative.
Even if the UK were to pull out and turn cap-in-hand to Uncle Spam yet again, who would pick up the UK's share of A400M costs? And don't forget the cancellation penalties which may well exist....
The UK has confirmed its support for A400M; France and particularly Germany now need to agree the way ahead. Which will not include any American alternatives.