Thanks for these, Jolan. Your ingenuity never disappoints.
Here is my stab at them.
1. Varsity said to be unmistakable (8)- UNIVOCAL? (Varsity – Uni with vocal – said = Univocal – unmistakeable)
2. Where the waist is firmly and irrevocably secured? (5,4,4)- UNDER ONE’S BELT?
2. (Double definition. Location of belt and phrase meaning secured. “Under your belt” would also fit.)
3. Provides a non-professional issue (4,2)- LAYS ON? ( Non-professional – Lay + issue – son gives lays on – provides.)
4. Don’t go away from scramble or dog events. Wait on. (5) SERVE? ( Subtractive anagram “Don’t go” away from “or dog events” with scramble as anagrind – serve – wait on. )
5. A light aeroplane meets Her Majesty and haughty ranking sister (6,8)- MOTHER SUPERIOR? ( Moth – light aeroplane+ Her Majesty- ER + haughty – Superior, gives Mother Superior- ranking sister.)
Thanks again.
AB