Most chefs, whether in a restaurant, or a pub, put their own little twists and garnishes on dishes. I would think that anyone with an allergy/intolerance to certain ingredients would be very specific when ordering their food. Likewise, anyone with a dislike for certain foods should make it very clear when ordering that they want a plain sandwich, or whatever, with no garnish/sauce, etc. It is the responsibility of the person ordering to make it quite clear what they want, and not expect the waiting staff, or chef, to know your specific preferences. If your food arrives with a sauce that you specifically said you didn't want, then you just simply send it back.
You are worrying about a hypothetical situation where, potentially, a person with an allergy could've eating your bacon & brie, with a sauce they are allergic to ... but you aren't a person with an allergy, and you didn't alert the staff to any intolerance, so there is no problem, is there? You simply didn't like the chilli jam, but I'm assuming you didn't specify that you wanted your sandwich completely plain, with no garnish, did you? Other customers, myself included, who are presented with a completely plain sandwich, with no garnish at all, may think it very boring, and that the chef hadn't made any effort to make his food more appealing. They can't be expected to automatically know everyone's preferences, unless they are told.
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Is there such a thing as delicious ready meals?
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