Mike Hill Labour Jill Mortimer Conservative A by-election for the House of Commons constituency of Hartlepool in the former county of Cleveland, England, was held on 6 May 2021.

[5] It became only the second time since 1982 that the UK governing party gained a seat in a by-election,[5] and was the first Conservative win in the constituency since its creation in 1974, with a majority of 6,940 votes.

The seat includes the town of Hartlepool itself and the nearby villages of Hart, Elwick, Greatham, Newton Bewley and Dalton Piercy.

[14] On 17 March, Reform UK leader Richard Tice, who contested the seat in 2019, told LBC that the party intended to stand a candidate.

[15] On 31 March, the party selected businessman John Prescott (no relation to the former deputy prime minister of the same name) as their candidate.

[18] Later that month, it selected as its candidate former Labour MP Thelma Walker, who represented the West Yorkshire constituency of Colne Valley, but lost her seat at the 2019 election.

[24] On 26 March, the Conservative Party selected farmer and Hambleton District Cllr Jill Mortimer as its candidate in the by-election.

Incumbent Conservative Tees Valley Mayor Ben Houchen was reportedly unhappy with the choice of candidate, due to her not being from the area, and declined to endorse Mortimer at the time of her selection.

[31] On 6 April, former journalist and local businesswoman Samantha Lee announced her intention to stand as an independent candidate lobbying for Hartlepool to be awarded freeport status.

[37] While Williams was a vocal advocate of a second referendum on EU membership, the constituency of Hartlepool supported Brexit by almost 70%; he was criticised when it was discovered that he had deleted his pro-EU tweets before his candidacy.

[39] He was defended by Starmer, while Labour peer and former shadow Attorney General Shami Chakrabarti called for him to be replaced "immediately".

In a letter to Conservative Party Chairman Amanda Milling, Rayner requested the publication of a "full account" of Mortimer's time living in the Cayman Islands.

"[53][54] In response, 1,400 people signed an online petition calling for the government to prohibit sex offenders from standing for public office.

[64][65] Attention was especially focused on the idea that voters did not know what Starmer stood for, a conclusion Williams and Labour deputy leader Angela Rayner both agreed with.

[66][67] On 23 August, Business Insider reported that Boris Johnson likely breached the Ministerial Code by using taxpayer funds to take a private jet to campaign in Hartlepool.