Starting with a premise that does not exist makes little sense. There is no global Britain. It is another red, white and blue. Scotland is looking to take the blue bit away and it is difficult to see how N Ireland can survive without continuing development of cross border trade and collaboration. Whether leavers are yet ready to accept that Britian just got smaller and less influencial is interesting because the signs are enthusiasm for Brexit is in decline, leaving the fundmentalists to bawl louder and louder.
An increasingly centralised Britian is not the answer. Forces are moving in the other direction. In the real world maximising the benefits of international interdependence and collaboration are the way to achieve a global reach