By Tom Rayner, digital politics editor
Metro mayors and city mayors are now among some of the most recognisable faces in English politics.
According to the polling organisation YouGov, the current mayor of London, Sadiq Khan, is more widely known to the UK public than his party leader Sir Keir Starmer.
The rollout of metro mayor positions since 2015 has been intended to devolve more powers from central government to city regions - like has been the case in London since 2000.
Although the specific powers and levels of funding available to metro mayors depend on the individual devolution deal agreed with central government, the roles all come with significant scope for decision-making and substantial budgets.
The combined authorities they run, like the Liverpool City Region and Greater Manchester Authority, are comprised of multiple local councils.
The metro mayors are able to set strategy in a range of areas, from housing and transport, to business support and economic development.
In addition to eight metro mayor contests on 6 May, there will also be five city mayoral elections. These mayors will become heads of single city councils, and have a remit to deliver public services within their local authority.
What influence do metro mayors have?
In addition to the powers they wield in their region, the coronavirus pandemic has thrust metro mayors into the national spotlight.
A good example of this over the course of the last year has been Andy Burnham's very public spats with central government.
The incumbent mayor of Greater Manchester spent weeks in the headlines last autumn as he battled with Boris Johnson over regional tier restrictions and the levels of funding provided in the government's COVID-19 support packages.
By using the disputes to question the prime minister's wider levelling-up agenda, the incumbent mayor of Greater Manchester forced himself into the national conversation.
In 2017 he won with 63% of the vote - if Mr Burnham can boost that this time around it will be a notable example of how devolved seats of power in England can be used to build personal political capital.
That said, the 2019 general election saw an increase in the number of Conservative MPs elected in the Greater Manchester area - with the constituencies of Bury North, Bury South and Bolton North East all turning blue. Could that shift be reflected in the mayoral vote this time?
Here is a full candidate list.
What wider story could the races tell?
Conservative mayoral victories in Tees Valley and the West Midlands in 2017 became seen as early signs that the so-called 'red wall' seats that Labour once considered their heartlands were beginning to crumble.
Andy Street, the former John Lewis boss who is the current Conservative mayor of the West Midlands, won by a narrow margin - with just 0.8% of the vote separating him from the Labour candidate Sion Simon.
This time he faces Labour's former chief secretary to the treasury, Liam Byrne.
If Andy Street can win again, it will demonstrate two things: that the government's handling of the pandemic has not hurt Conservative electoral fortunes too badly, and that Sir Keir Starmer's efforts to rebuild Labour's prospects have suffered a severe blow.
Equally, if Mr Street loses, questions will be asked about whether the increased support for the Conservatives in the West Midlands, seen in the 2019 general election, may be on the wane.
Here is a full candidate list.
What are the other key races?
Tees Valley: Can the 'blue wall' hold?
Ben Houchen's election as the first mayor of the Tees Valley in 2017 was a significant moment - a 30 year-old Conservative local councillor had won high-profile public office in Labour's traditional industrial heartland.
It has since been described as the "first blue brick in the red wall".
Now all eyes are on whether Mr Houchen is able to retain his position as poster boy of the new Conservative popularity in the North East.
In 2017 he was up against candidates from Labour, the Liberal Democrats and UKIP - this time it is a two-way fight with Labour's Jessie Joe Jacobs as other parties have chosen not to contest the election.
Turnout could be a big factor in this race. In 2017, Mr Houchen won on a turnout of just 21%. This time around there is a critical parliamentary by-election in Hartlepool, which is part of the Tees Valley mayoral area.
A significantly increased turnout makes the likely result more difficult to predict, but the expectation of many analysts is that Mr Houchen will win re-election.
London: Can Khan win in the first round?
There are a record-breaking 20 candidates standing to take control of City Hall in these elections.
But if polling is right, the incumbent Sadiq Khan is set to equal the electoral achievement of his predecessors Boris Johnson and Ken Livingstone and win a second term.
What would set Sadiq Khan apart, however, is if he is elected with an absolute majority.
Voters in London get to register a first and second preference for who they want to be mayor. If a candidate wins more than 50% of the first preferences they are automatically elected. If they don't, all candidates apart from the top two are eliminated and the second preference votes are counted to establish a winner.
Since the role was created, no candidate has won in the first round, but there are fears in Conservative party headquarters that Shaun Bailey's campaign has struggled to get traction with voters.
A first round loss would be a major embarrassment for the party and Mr Bailey.
Here is a full list of candidates
West Yorkshire: A Labour certainty?
People in Bradford, Calderdale, Kirklees, Leeds and Wakefield will be voting for a metropolitan mayor for the first time.
The favourite to take charge of the West Yorkshire Combined authority is Tracy Brabin - the current Labour MP for Batley and Spen.
The election will be contested by seven parties in all: Labour, the Conservatives, Reform UK, the Yorkshire Party, the Green Party, the Liberal Democrats, and the English Democrats.
It would be a real upset if the shadow minister for cultural industries did not win.
But if Labour's results in the wider spread of the 6 May elections are looking bad, this race could garner more attention.
Why? Because as things stand it is expected to be one of the last results to declare - with a result possibly not announced until Sunday 9 May.
If things are going wrong for Sir Keir Starmer around the rest of the country, the wait for confirmation of a victory in West Yorkshire could be a nervous one.
Here is a full list of candidates.
Bristol: Confusion between city and region?
The Bristol city mayoral election is about who will lead the city council, rather than the regional area.
Marvin Rees, the Labour incumbent, was first elected as Bristol city mayor in 2016 but his profile has increased over the course of the last year as a result of the national attention on Black Lives Matter demonstrations in the city.
But voters in Bristol will also be asked to decide who they want to be mayor of the West of England.
A recent survey by the Centre for Cities found only 7% of residents could name Tim Bowles, the current Conservative mayor who is not standing for re-election. Some 79% said they didn't know there was a regional mayor and the remaining 14% gave an incorrect name - mostly that of Marvin Rees.
During a recent campaign visit to the region, the prime minister himself was unable to name Mr Bowles or Samuel Williams - the Conservative candidate standing this time around.
What impact could this confusion, or lack of awareness about the role, have on the vote for West of England mayor?
It's already expected to be a tight contest. Labour will hope to benefit from the fact there are council elections being held in Bristol, but not in other areas in the region such as Bath and North East Somerset.
This could see turnout lower in areas where the Conservatives would be hoping to pick up more votes.
But despite that potential advantage, Labour's ambition to win both the city and regional mayoralties could be put in check by signs of growing support for the Green Party.
When the regional mayoralty was last contested in 2017 no candidate won an absolute majority in the first round, which meant the result was determined by second preference votes.
If that happens again, the distribution of second preference votes for the Green and Liberal Democrat candidates could be decisive.
Here is a full list of candidates for the city mayor and the metro mayor race.
Liverpool: Will local turmoil test party loyalty?
Labour's Steve Rotheram is another metro mayor who gained national prominence over the last year due to the COVID-19 pandemic.
Like Andy Burnham in Greater Manchester, the mayor of the Liverpool City Region regularly clashed with central government over coronavirus policies.
The City Region is made up of six local councils, all of which are Labour strongholds, so the former MP is expected to win re-election relatively easily.
Pic: Harry Whitehead/Shutterstock
Pic: Harry Whitehead/Shutterstock
However, one thing to look out for is whether his majority goes down from the nearly 60% of the vote he won in 2017.
Labour has been beset by corruption controversies in Liverpool in recent months following the arrest and resignation of the former city mayor, Joe Anderson. He denies any wrongdoing.
The party has been embroiled in further chaos in the efforts to select candidates to replace Mr Anderson.
Three serving councillors who had initially been shortlisted for the candidacy were excluded at the last minute by Labour HQ, much to the ire of some local party members.
The race for city mayor and the metro mayor positions will be a test of how far those events have tarnished Labour's reputation in what has arguably always been its most loyal city.
Here is a full list of candidates for the metro mayor race and the city mayor race .
When will we know the results?
As with the other council and national parliamentary elections taking place on 6 May, the results of the city and regional mayoral races are expected to come in over the course of the weekend.
A result for mayor of Doncaster could come overnight on Thursday, but in most cases it will take a bit longer.
In London, for example, counting will be split over two days. This means there should be a result on the evening of Saturday 8 May, but that could potentially slip to Sunday 9 May.
The earliest metro mayor result could be Tees Valley on the evening of Friday 7 May, with the rest expected through Saturday and Sunday.