It's a pun ... a terrible, terrible pun.
Penne is pronounced "pennay" in the UK in my experience, making this pun kinda dysfunctional.
Also as pointed out, UK cryptic crossword answers are phrases in actual use, not new word combinations.
Edit to add relevant example:
See 9 across ("Rotten people sin to produce malicious missive") here: https://www.fifteensquared.net/2021/03/08/independent-10733-...
I also noticed that "poisoned pen" isn't a phrase in British English, instead it's "poison pen" or more typically "poison pen letter".