Unilaterally (from the W’minster side) put Scotland (as a kingdom), Wales (as a principality), Mann (as a lordship), insular Normandy (as a duchy) and Ulster (as a Free State) on an equal footing with 1932 Canada, except that they have the right to make constitutional legislation by means of referendum, including stripping Westminster’s right to legislate on constitutional matters. Referendums in the colonies (yes there still are some) must be used to dispose of them, according to the options of condominium with all the independent states, or subjection to just one, or secession (only Bermuda would realistically have a chance).
This way, England gets to have the national reckoning it really needs relating to resource availability and feeding itself, and the other countries (except Wales with Llyn Celyn - Liverpool could be annexed to Wales, instead) get to continue or break ties with England as needed.
Wen