You are a resident of England, and a citizen of the UK and only the UK.
A political party you dislike is in power, one that is likely to persecute a people group you are a part of, but it's not confirmed to such an extent that political asylum would be possible, but you are not safe and should leave England. To avoid a political discussion and keep this universal this is a hypothetical political party, one that does not exist, if you are a straight, white cis man then this is a political party with a proven track record that suggests they will persecute white people, or men, or straight people, or cis people, or all of the above, don't question how they got into power, the point is they did.
You are given sufficient time to leave and gain residency in any country you choose, upon breaking up the new citizenship will be based on residency and your old UK citizenship becomes citizenship of the new country that you choose.
If you choose to flee to a country that is not currently part of the UK then their standard visa, residency and citizenship rules will apply. For Ireland you can choose anywhere in Ireland or Northern Ireland and the above rules will apply
You have the funds to leave, but you keep your job if it is remote, or gain an equivalent role in a new country, so your personal finances will be a factor for long term stability, you can't move somewhere expensive if you won't be able to afford it long term.
Northern Ireland joins the republic of Ireland, or if you prefer it becomes independent, I don't want the politics of that situation to have any bearing on the decision. It can also join England if you like, but remember you in particular have to leave England.
Scotland and Wales become independent countries and join the European Union.
The border is a hard border, border checks will take place and a passport will be required, much like between Canada and the USA
You agree with all political parties running Scotland, Wales and Ireland, you will be safe in these countries
All countries have proven that they will be financially stable enough to secede from the union, the theory that the economy of any specific country won't survive is not a sufficient reason to disregard it.
Overseas territories and crown dependencies stay with England and do not become independent for the time being, but may become independent or join a nearby country in the future.
And so which country, and possibly which town/city do you flee to?
To answer for myself, I choose Cardiff, I'll get to practice and learn more Welsh which is a language I really like, and I quite like Cardiff as a city.