Hello and welcome. It is always good to hear about new projects on Altverse. I find it an interesting idea to develop, although I think you have a lot of work to do. The United Kingdom is not a minor country and its historical importance and influence have been (and are) very great, so it will be necessary for you to build a well-founded historical background. What happened to the second world war? It is something that, for example, needs to be clarified. An authoritarian state outside the "democratic" canons of Western Europe probably were not on the allied side. And if that were not so ... the outcome of the war would have completely changed affecting the history of all Altverse. It is necessary to work together on aspects of your story that may affect global history.
In addition, it would also be interesting to see how this nation's relations with the rest of the world are today. Being an authoritarian nation, it will be very interesting to see how it is accepted or not by Western democracies. Finally, and depending on diplomatic relations, there is the economic issue. Britain is an economic power mainly because of its great openness and economic liberalism, something that will be difficult to justify under a closed and authoritarian regime. Without economic prosperity there is no power of any kind.
In any case, if you continue with the project...