24 across (7) P?O?E?? Make prdiction for aircraft going over speed of light. 16 down (3)(5) ?E? O???R. A ring held by me,say, for marine mammal. Also, 7 down looks as if it must be "edifice" but why?
Many thanks to all who replied. Sorry to be so long in ackowledging all your efforts but my PC has been behaving rather oddly. BT hub problems, I think - all seems to be well now.
Apologies to fiction - factory - I should have remembered that not everyone has the relevant crossword grid in front of them!