This is a prime example of how it should be the prime directive for the country to reach a prime number of states. This can be taken on as the prime responsibility for the prime minister (if you had one…you should make one).
United Kingdom: recreate the English heptarchy, keep Scotland, Wales, and Northern Ireland as separate things, and then give London autonomy too. Now we have 11 that are all of a similar scale. Cumbria becomes part of Scotland and Cornwall becomes part of Wales to account for the parts that weren’t in the heptarchy. If Northern Ireland unites with the rest of Ireland, we create a united body to represent the crown dependencies and overseas territories and count that as the 11th