United Kingdom of [1] England, [2] Wales, [3] Scotland, [4] Ireland, [5] Nova Scotia, [6] Prince Edward Island, [7] New Brunswick, [8] Newfoundland-and-Labrador, [9] Quebec, [10] Ontario, [11] Manitoba, [12] Saskatchewan, [13] Alberta, [14] British Columbia, [15] Queensland, [16] New South Wales, [17] Victoria, [18] Tasmania, [19] Southern Australia, [20] Western Australia & [21] New Zealand
Unitary state like OTL nowadays UK but with 21 , not just 4 "home nations".
Each home nation has its devolved regional power structures, but only as delegation of the Westminster Parliament power.