AFAIK, there are two companies involved in impoering magazines,etc from aborad ( I think Easons is one of them) and they provide a ready reckoner of how stg prices should be refelcted in euros. It bears absolutely no relationship to the normal exchange rate and has a generous built in cushion against fluctuations.
If I recall correctly, the Competition Authority in its early days sought to do something about what, on the face of it, looks like price fixing. But I think the addition of the catch-all term "recommended price" overcame the legal hurdle. In other words, retailes are fre to charge less, but in reality, they just refer to the ready reckoner.