Thanks for these, Jolan. Enjoyable and devious as always. Great clues.
Here is my stab at them.
1. The business jets may tap cash supply (3,4,7) – THE CAT’S PYJAMAS?
(Anagram of “jets may tap cash” can “supply” “the cat’s pyjamas”- the business?)
2. Train robbery? (5,2)- BREAK IN? (Double definition – to train an animal is to break in and a break in is a robbery?)
3. Fiercely dig with club, ending up with nothing (4,5-1)- LIKE BILLY-O? (Dig – like, with club, billy and O- nothing gives “Like billy-o” – fiercely?)
4. It describes an action in those who favour a book (8)- PROVERBS? (It describes an action – verb, inside “those who favour” – pros, gives Proverbs, a book in the bible?)
5. Predisposition to abolish the poorest, perverted and weak (7)- INSIPID? ( Subtractive anagram – predisposition minus poorest , perverted, gives insipid – weak.
Thanks again.
AB