1 across. One ‘doing’ another? 13 letters.
8 across. Door opener? 4 letters.
9 across. Flying. 8 letters.
10 across. Beneficial – take a bow! 4 letters, 3 letters and 3 letters.
12 across. Fish-eating hawk. 6 letters.
14 across. Boss – of the kennel club? 3 letters and 3 letters.
15 across. Mouth tissue. 4 letters and 6 letters.
19 across. France or the USA, but not the UK. 8 letters.
20 across. Part. 4 letters.
21 across. No-longer-runny breakfast? 4-6 letters and 3 letters.