I grew up in israel with a nusach sefard pronounciation. Then I moved to England, where I was told to follow my fathers minhag - ashkenazi. I regret not checking this earlier, but what havara should I have? People are very accepting of whatever i choose (not triggering arguments), my fathers ashkenazi, but it is easier for me to read nusach sefard. Also, can you please give me some ashkenazi halachic authorities who talk about this to look at for more detail please?

Shalom, if you say that it's easiest for you to use the sefaradic/Israeli pronunciation on which you grew up, then that's what's best for you (it also sounds from your last name that your real family origin may be Italian or Sefaradic descent, and apparently not ashkenazic, and accordingly that's your real and original family custom). Especially in a place like England where, as you say, there's no one totally accepted pronunciation. Also, it's not uncommon for your (future?) children to be embarrassed of using an ashkenazic pronunciation, which is often seen as more "old-fashion", and their understanding of Hebrew (one of the most important aspects of tfila/prayer) is probably learned with the Israeli pronunciation (especially if you are originally from Israel, so BH Hebrew may be understood very well in your personal home), and these are additional important factors to take into account (that they and you should feel comfortable & understand more- to feel they are "speaking" to Hashem). In addition, statistically (see online demographer Prof. Sergio Della-Pergola), as time passes, by the end of the 21st century, over 80% of the Jews (more than 20 million) will be in Israel, only about 4 million outside (almost all in America), and the odds are that your children growing up in England will inevitably wind up living in Israel (especially in your case where you apparently have relatives here), so that's also connected with the aforementioned factors. In addition, linguists, historians, kabbalists and almost all rabbis agree that the Yemenite (which is closer to Sefaradic) pronunciation is the most accurate and original, for: 1. They didn’t move around and were less prone to outside influence, compared to Jews in the other exiles. 2. Hebrew is obviously similar to the other Semitic languages, and the Yemenite is most similar to Arabic and other Semitic enunciations. 3. The Yemenites have a different sound for every single letter (pretty logical!), even a variant sound for every letter with a dagesh, as opposed to the Ashkenazim who illogically say "alef" like "ayin", and “tav” without a dagesh like “samech”, or Moroccans who pronounce it like “tet”, and both say “caf” with a dagesh like “kuf”, and "bet" without a dagesh like "vav", etc. Why would God (Who created would be a Hebrew) have so many letters for the same sound?! 4. The Zohar goes into precise detail and explanation how the mouth, teeth, lips and throat pronounce each letter and it is clearly the Yemenite way. This doesn’t mean that everyone has to start saying Kriyat Shma or Parshat Zachor like the Yemenites, but in your case, this is nother advantage of the Sefaradic, as opposed to ashkenazic, enunciation. For sources, see R. Chaim David HaLevy, Shu"t Aseh L'cha Rav v, 20 and 100.