[6][8] Proudfoot was inspired to found the party after watching Andy Burnham's critical response to the Westminster government's support package for Greater Manchester during the COVID-19 pandemic.

[6] He told Big Issue North that the centralisation of power in London had played a part as well, highlighting the North-South divide in healthcare, transport, education, and general standard of living as motivating factors.

[3] Following the NIP announcement that it had selected former Labour MP Thelma Walker as its candidate for the Hartlepool by-election in May 2021, it was reported by Huffington Post UK that the party's membership had increased from 300 members to 1,300.

[15][17] Proudfoot has said that the geography of Northumbria would consist of Yorkshire, Lancashire, Cumbria, Merseyside, Tyne and Wear, Greater Manchester, County Durham, Northumberland and Cheshire, and, since 2022, has generally included the borough of High Peak in northern Derbyshire within it.

[23] Identifying itself as a post-Brexit party, the NIP's draft manifesto stated that an independent North could make a decision to join the European Union via a referendum "in the distant future".

"[26] In an opinion piece for The Times, former Labour staff member James Matthewson called the NIP "a glorified joke" and accused it of being a "fetishisation of Northern working-class culture by privileged, middle class hard-left ideologues".

[27] Labour MP for Liverpool Riverside, Kim Johnson, dismissed the party's slogan, 'It's About Bloody Time', and use of a logo featuring a whippet as "patronising in the extreme".

[28] Writing for Novara Media, psephology blogger Ell Folan, though dismissive of Thelma Walker's chances to win Hartlepool, believed the NIP "could easily cost Labour key seats in the future (especially with the Tories so far ahead in the polls)", concluding that "with leftism still popular in the north, regionalism on the rise and Labour's red wall no longer solid, Starmer needs to take the NIP seriously – or it won't seem like a joke much longer".