What is 2021 Hartlepool by-election?
{{Infobox election | election_name = 2021 Hartlepool by-election | type = parliamentary | country = United Kingdom | seats_for_election = [[Hartlepool (UK Parliament constituency)|Hartlepool]] constituency | turnout = 42.7% | ongoing = no | previous_election = 2019 United Kingdom general election | previous_year = 2019 | next_election = Next United Kingdom general election | next_year = ''Next'' | election_date = 6 May 2021 | candidate1 = '''[[Jill Mortimer]]''' | image1 = {{CSS image crop|Image =Official portrait of Jill Mortimer MP.jpg|bSize = 120|cWidth = 120|cHeight = 160|oTop = 0|oLeft = 0}} | party1 = Conservative Party (UK) | last_election1 = 28.9% | popular_vote1 = '''15,529''' | percentage1 = '''51.9%''' | swing1 = {{increase}} 23.0% | candidate2 = [[Paul Williams (Labour politician)|Paul Williams]] | image2 = {{CSS image crop|Image =Official portrait of Dr Paul Williams crop 2.jpg|bSize = 135|cWidth = 120|cHeight = 160|oTop = 12|oLeft = 6}} | party2 = Labour Party (UK) | last_election2 = 37.7% | popular_vote2 = 8,589 | percentage2 = 28.7% | swing2 = {{decrease}} 9.0% | candidate3 = Sam Lee | image3 = {{CSS image crop|Image =|bSize = 120|cWidth = 120|cHeight = 160|oTop = 0|oLeft = 0}} | party3 = Independent politician | last_election3 = ''New candidate'' | popular_vote3 = 2,904 | percentage3 = 9.7% | swing3 = ''New candidate'' | map_image = Hartlepool2007Constituency.svg | map_size = 250px | map_caption = Location of [[Hartlepool (UK Parliament constituency)|Hartlepool]] within the former county of [[Cleveland (county)|Cleveland]] | title = [[Member of Parliament (United Kingdom)|MP]] | posttitle = | before_election = [[Mike Hill (British politician)|Mike Hil