2018 local elections: How the BBC is reporting the results

All the elections taking place on Thursday 3 May are in England. 150 councils are electing new councillors, and there are six mayoral contests.

They include all the seats in all 32 London boroughs, as well as every seat in the metropolitan districts of Birmingham, Manchester, Leeds and Newcastle.

A third of seats are up in 30 other metropolitan districts, including Liverpool, Sheffield, Sunderland and Wigan.

There are 67 district council elections. Seven of them have all the seats up for grabs, six of them have half and the remaining 54 are electing a third of the councillors.

There are also elections for 17 unitary authorities. Blackburn with Darwen and the Hull City Council have all their seats up, while the remainder are electing a third.

Individual by-elections to fill a vacant seat on a council can take place at any time throughout the year. Check your local council website for details.

There's a metro mayor election for the new Sheffield City Region as well as five council mayors. The Sheffield City Region encompasses Barnsley, Doncaster, Rotherham and Sheffield.

The five council mayors will be elected in Hackney, Lewisham, Newham, Tower Hamlets and Watford.

If your council elects in thirds, it means that a third of councillors are up for election every year over a four year cycle, with one year when there are no elections. The councillors elected this year will serve a term of four years.

Some of the councils that elect in this way cannot possibly change overall control, because the existing majority for the controlling party is larger than the number of councillors they could lose.

Some councils hold elections for half of their councillors every two years.

Other local authorities, like those in London, hold an election every four years for all of their councillors. Councils which have had boundary changes usually elect all of their new councillors at once.

If a party has a majority of councillors on any particular council, it is deemed to be in control of that council.

If no one group has a majority it is described as "No Overall Control" (NOC) or "Hung".

So if there are 20 Labour councillors, 15 Conservatives and 10 Lib Dems in a ward with 45 councillors, it is still NOC even though Labour has more councillors than any other party, because they can't outvote the other parties by themselves.

Council control prior to the election has long been defined by the BBC, the Press Association (PA) and others as which party, if any, has a majority on the eve of the poll.

So if a council was won by the Conservatives in 2014, but then through defections and by-election losses became No Overall Control, in 2018 we would describe it as a Conservative gain should the party regain its majority.

Seat change is based on how many seats each party won at the previous comparable election, not what the seats were on the eve of the election.

For most of the seats up this year, the previous election was in 2014.

In some councils, boundary changes come into force in 2018 where councils are reorganised and the number of seats on the council changes. More on boundary changes further down...

In cases like this, the BBC uses "notional results" to project what the previous result would have been if the new boundaries had been in place at the last election.

The total number of seats per party will be slightly different between the seats-at-dissolution and those won at the last election.

You vote for councillors in the ward you live in, who come together with councillors elected in the other wards in your council area to run the services the council is responsible for. Depending on where you live, you may have to vote for more than one candidate to represent your ward.

Wards are the smallest electoral division used in the UK. They vary in size substantially, but have an average electorate of around 5,500 people. For the councils up this year, there is an average of 50 councillors per council.

The largest council up for election this year, Birmingham, has 101 councillors across 69 wards, down from 120 councillors in 40 wards at the last election.

Redditch, also in the West Midlands, is one of the smallest councils up this year. It is electing 10 of its 29 councillors this year, across 12 wards. Residents of the other two wards will not be able to cast a vote this year.

Every now and then councils review whether they have too many or not enough councillors. This can be instigated either by the councils or by the Local Government Boundary Commission.

Councils also occasionally re-draw ward boundaries internally, without increasing or reducing the overall number of councillors. This could be to even up the populations in each ward in areas where new housing estates have popped up or where lots of people have left the area.

There are no strict rules on how many people should live in each ward, but if they are too unbalanced it means some votes are effectively less powerful than some others.

If you wake up at 6am on the Friday after the election, you will be able to find results for about 99 councils on the BBC website. The remaining 51 are scheduled to come in throughout the Friday, mostly between midday at 6pm.

If you're planning to stay up all night and follow the television coverage, we expect the first full councils to be declared at about midnight. One of either Swindon Council, or Halton in Cheshire, is expected to be first to declare its results.

The most active period is between 2 and 3am when more than 40 councils are expected to declare their results. This includes the big metropolitan councils of Liverpool and Sheffield. Birmingham and Manchester are not expected until later on in the afternoon of the next day, Friday 4 May.

The BBC does not report the results of council by-elections or parish council elections. Check your local council website for details.

There are different types of councils across the UK and they hold elections at different times.

There were elections in all local councils in Wales and Scotland last year, and Northern Ireland will elect all of their councillors next year. There were also elections in county councils across England last year.

Non-metropolitan district councils, also known as shire districts, are usually also covered by a county council. The county council controls the most expensive services like education, public transport, policing and fire services. Most English county councils were up for election last year.

The services devolved to the district councils include setting and collecting council tax, bin collections, local planning and council housing.

Unitary authorities are responsible for providing all the services that the district and county councils would provide.

Metropolitan district councils are more similar to unitary authorities in terms of the services they look after, but typically sit in built-up city areas. Unitary authorities are usually made up of smaller towns and the less urbanised areas surrounding them. Southampton, Peterborough and Hartlepool are three examples from this year.

London boroughs are more similar to shire districts. They organise social services, bin collections and local parks while the Greater London Authority (GLA), headed up by the Mayor of London, is responsible for policing, fire, and transport services. The responsibility for housing and road maintenance is shared by the boroughs and the GLA.

Some councillors for the party which holds power within a council will have a specific brief, like the councillor responsible for health and social services. Some councillors representing parties who aren't in control will hold opposition briefs and put forward alternative policies at council meetings.

Directly elected council mayors are the political leaders of the council with overall responsibility for the delivery of services. In councils without a mayor, a leader will be appointed from the elected councillors.

Not all local authorities have a directly elected mayor. Whether or not they have one is decided by the authority itself, often after a local referendum.

The 'metro mayors' - or combined authority mayors - are different. The Sheffield City Region mayor will be the eighth person elected to head up a combination of local authorities.

London has had one since 2000 and six other areas, including Manchester, Liverpool and Birmingham, elected mayors for the first time last year.

Their responsibilities differ, but the website for the Sheffield City Region combined authority says the new mayor will "be an ambassador for the area; promoting it as a place to live, work, visit and invest in." There isn't an agreed budget yet, because of a disagreement between the local authorities which make up the Sheffield region.

The six metro mayors elected last May are each responsible for a 30-year investment fund.

NOC: No overall control - no one party has a majority of seats on the council. Also referred to as a "Hung Council"

CON: Conservative

LAB: Labour

LD: Liberal Democrats

UKIP: United Kingdom Independence Party

GRN: Green Party

ICHC: Independent Community and Health Concern

BNP: British National Party

RA: Residents Association

IND: Independent

OTH: Others - people representing minor parties not covered by any of the labels above