What happened
Burnham framed the plan as "the biggest rebalancing of power our country has seen," positioning decentralisation as the organising idea of his platform rather than one policy among many. The proposal would relocate a genuine seat of governmental coordination to Manchester for the first time, rather than the more common practice of relocating individual civil service jobs or agency headquarters outside London.
The reaction has split along fairly predictable lines. The Scottish Green Party noted the speech was "clearly aimed at the English regions, with Scotland, Wales and Northern Ireland treated as an afterthought" — a fair critique given the proposal's explicit focus on the Midlands, Yorkshire, and the North of England specifically. From the right, critics argued devolution of this kind is "simply more Government: more state control, more layers of bureaucracy, more tax, more spending, and more politicians" rather than a genuine transfer of power. A more structural objection holds regardless of political direction: every mayoralty, combined authority, and devolved institution in England exists only because Parliament allows it to, and Westminster can alter, reduce, or abolish those powers whenever it chooses — meaning "Number 10 North" would have no constitutional protection against a future government simply winding it back.
As of publication this remains a leadership pitch rather than government policy: Burnham was not yet Labour leader or Prime Minister, and the outcome of the contest was not yet decided.