BA sells from M&S so no Kosher food.
Easyjet has kosher bagel with salmon and cottage cheese to buy on board on all routes to and from TLV.
Assuming you’re flying economy, their ‘Buy on Board’ menu is listed online.
However, it doesn’t specifically indicate which, if any are kosher, and presumably that exercise is left up to the reader :/
Indeed, in their FAQ when asked:
Are there any options for specific dietary requirements?
All they say is:
Yes, you will able to find vegetarian and gluten-free options in the
M&S on board menu.
Credit:stackoverflow.com‘