It’s all one turn. There is no separate Europe UK and Pacific turn its all one turn. So all UK units move once. The only thing that is separate is purchasing and placing units. UK is one country just like germany is one country and Russia is one country and japan is one country. The only thing different about UK from everyone else is you keep your purchases separate and your unit placement separate on the europe and pacific side of the boards.
So you purchase for the Europe UK and Pacific UK on the same turn. Keeping the money from each board separate. Then at combat movement phase it becomes one entity just like all the other countries. At the CM and NCM there is no Europe UK and Pacific UK there is just the UK. Does that help?
Then when you place units and collect money you once again keep the economies separate as well as unit placement. What UK pacific buys can’t be placed on the European side of the board and vice versa.
So once again UK is one entity you don’t move twice and they are not two separate powers as far as movement of units on the board is concerned.