Royal awards ceremony's ending in hour: Britons had to be decorated (8,7)
I believe the answer is:
birthday honours
'royal awards' is the definition.
(honours given out by the monarch on their birthday)
'ceremony's ending in hour britons had to be decorated' is the wordplay.
'ending' indicates one should take the final letters (the ending of the word).
'in' indicates putting letters inside.
'to be decorated' indicates anagramming the letters (letters decorated or arranged differently).
The final letter of 'ceremony' is 'y'.
'hour'+'britons'+'had'='hourbritonshad'
'hourbritonshad' is an anagram of 'birthdahonours'.
'y' placed within 'birthdahonours' is 'BIRTHDAY HONOURS'.
(Another definition for birthday honours that I've seen is " Titles conferred by the Queen each June".)