We're less than a week into Andy Burnham's premiership of the UK, but a massive structural move has already been made: opening a second seat of government in the northern city of Manchester. 

Here's what it is, why it's happening, and the reactions to the so-called King of the North's new castle.

What is it?

No. 10 North is a northern outpost of Whitehall's famous Downing Street, making it the first working prime ministerial office outside London in the modern era. 

It's effectively a second seat of government that Burnham hopes will spearhead the devolution of power away from Westminster, becoming the "engine room of devolution and good growth in every postcode."

Describing the move as "not a gimmick", the government aims to put regional mayors and local leaders closer to the policy decisions that affect their areas, rather than routing everything through Whitehall, to ultimately transform the UK's North-South divide.

What will it look like?

Well, don't expect a second black door! 

The interim home of the project is Heron House, a 123,000 sq ft, six-story government building on Albert Square in central Manchester, currently shared with the Government Communications Headquarters, or GCHQ. The offices are already operational, being officially launched on July 24 by the prime minister and new finance minister John Healey. 

However, Heron House remains a temporary base, with the longer-term plan involving a relocation to a new digital campus that is currently being built in Manchester's Ancoats area, on a brownfield site. Maybe a new door could be installed there?

While the development of this space isn't expected to be completed for another six years, Whitehall civil servants are already being offered relocation packages to Manchester, according to reports. 

Who will run it?

Political oversight will sit with Louise Haigh, the UK's First Secretary of State and key Burnham ally who also leads the newly created Office of the Prime Minister and Cabinet. 

On the ground however, Burnham's 'right-hand woman' Caroline Simpson will be running the show. The outgoing CEO of the Greater Manchester Combined Authority has spent years working alongside Burnham during his time as mayor, and so the appointment remains inline with the PM's tendencies to favour 'Manchesterism'.

Burnham himself has promised to work from Manchester at least once a week – something he will likely look forward to, given that his wife and family are remaining in the city.

How much will it cost?

According to Burnham's government, nothing. This is because Heron House is an existing government building already used by GCHQ, meaning there is no major new capital cost for the interim site.

However, additional accommodation, protection and security for a second prime ministerial site, staff relocation packages, and ministerial travel between London and Manchester will all add up. Factor in the development of the digital campus in Ancoats, and that bill gets all the more longer. 

What are the reactions?

The plan, like most plans, has split opinion sharply along political lines: Burnham's insistence that the move is "not a gimmick" has fallen on deaf Conservative ears, with Leader of the Opposition Kemi Badenoch saying the prime minister is "acting as if he is still the mayor of Manchester".

Nigel Farage, leader of the far-right Reform party that has been snapping at Labour's heels in recent by-elections, has been openly skeptical, warning that a No. 10 in the south and a No. 10 in the north would lead them to "naturally fight against each other."

In contrast, political think tank, the Institute for Public Policy Research North, has welcomed the plans, with a spokesperson saying that the country needs "a decentralised government with branches around the country and that listens to people."

What's next?

It's hard to say. While Burnham has only just embarked on No.10's postcode change, his mission to rewire the British government will be no mean feat. 

It's clear that the "King of the North" wants to keep his throne warm – but whether the power, money, and decisions actually follow him there is yet to be revealed.