23. down.
Starter of mutton scoffed by priests in RC feast once (6) ( L?G?A?).
24. down.
Scene imagined blowing a gasket close to Watford Gap services, possibly? (6)
7. down.
US president with nothing in diary, apparently (5) (?I?O?). (M?I?G?).
20. down.
One admitting failure at the outset -- probably not working out? (5) (?N?E?).