I made Jet2 aware of son’s anaphylactic allergy before we flew (peanut) via telephone. (7/2019).
On boarding both flights the crew confirmed they knew about his nut allergy and an announcement would be made and no nut products would be sold. They did exactly this and we had no issues.
I did think the announcement sounded pre-recorded which suggests they are fully aware of the need (and are prepared to) to assist passengers with allergies.