Based on this metastudy titled Epidemiology of anaphylaxis in Europe, they found the prognosis was:
> Case fatality rates were noted in three studies at 0.000002%, 0.00009%, and 0.0001%.
That's among all cases of anaphylaxis, so the answer is "they are almost nonexistent". It's not even a rounding error. Something on the order of a few dozen people per year for a country the size of the UK and from what I can tell, most of those are due to administration of IV medication where the allergy was previously unknown and much more severe.
Based on this metastudy titled Epidemiology of anaphylaxis in Europe, they found the prognosis was:
> Case fatality rates were noted in three studies at 0.000002%, 0.00009%, and 0.0001%.
That's among all cases of anaphylaxis, so the answer is "they are almost nonexistent". It's not even a rounding error. Something on the order of a few dozen people per year for a country the size of the UK and from what I can tell, most of those are due to administration of IV medication where the allergy was previously unknown and much more severe.
[1] https://onlinelibrary.wiley.com/doi/epdf/10.1111/all.12272