What's happening on Thursday?
There are local council elections in England and Northern Ireland - but the big one this year is the European election on the same day. It is the only time outside of a general election when all 46 million voters can take part. The European Parliament is the only directly elected institution in the European Union. So this is your chance to decide who represents you in Brussels and Strasbourg (Yes, they still shuttle between the two parliament buildings at regular intervals).
How do I know if I can vote?
Most people should have received polling cards through the post. To be eligible to vote, you had to be on the electoral register by 6 May. Anyone over 18 on 22 May who is a British citizen living in the UK, a qualifying Commonwealth citizen living in the UK, a citizen of the Republic of Ireland living in the UK, or an EU citizen living in the UK can vote if there is a local election where they live. British citizens living overseas can also vote in the European elections provided they have registered as overseas electors. EU citizens living in the UK can only vote in the European Parliament elections if they don't vote in their home member state.
How do I vote?
You can go to your nearest polling station on Thursday. It is normally a local school or community centre - the location will be on your polling card. You do not need to take the polling card with you in order to vote. A member of staff will give you a ballot paper with a list of candidates and parties on it. Put a cross in the box next to the ones you want to vote for. The deadline has passed for applying for a postal vote - if you did apply for one you can drop it off at the polling station. If you have a specific, long-term reason that you can't vote in person, such as a disability or being overseas, you can apply to allow someone to vote for you on the Electoral Commission website. If you are suddenly incapacitated or taken ill, you can apply to vote by proxy for medical reasons up until 5pm on polling day. Polling stations are open between 7am and 10pm.
The Electoral Commission is worried the current craze for smart phone self-portraits, as demonstrated above by the prime minister, will threaten the secrecy of the ballot. They have issued guidelines to staff at polling stations advising them to discourage the taking of "selfies", or any other kind of photograph in the polling station. There may be notices on the wall warning people about it. Taking a photograph in a polling station is not a criminal offence in itself, but sharing of information that appears on a ballot paper, even before it has been filled in, could represent a breach of Section 66 of the Representation of the People's Act 1983, leading to a fine of up to £5,000, or a six months jail sentence. It all depends on whether the photograph was shared with others and what is in it - but the Electoral Commission is not taking any chances. "Given the risk that someone taking a photo inside a polling station may be in breach of the law, whether intentionally or not, our advice is that you should not allow photos to be taken inside polling stations," says the guidance to staff. Tweeting pictures of a postal ballot is also discouraged.
Why do the local elections matter?
They are a chance to decide who runs your local services - everything from refuse collection to pavement potholes and children's services. The results can also send a signal to the parties at Westminster with a year to go before the next general election. There are elections in 161 councils in England and 11 in Northern Ireland.
Why do the European elections matter?
It is often ignored by the British media, but the European Parliament has a growing influence over our daily lives. It can not originate laws just revise or block legislation from the unelected European Commission, but it has more power than it used to, particularly in areas like consumer protection, the environment - such as the genetically modified crops German Greens are protesting against in the above picture. Nobody wins the European elections - there are no government and opposition benches like at Westminster. But the make-up of the new Parliament is likely to have a decisive influence on the future direction of the EU - particularly if, as expected, there is a large block of Eurosceptic MEPs. In the UK, the result can have a big impact on a party's mood and their leader's prospects ahead of the 2015 general election. Check out their election broadcasts to get a feel for how they are pitching it.
So how does the European voting system work, exactly?
Britain is one of eight countries - including Germany and France - to use a "closed list" system. So you vote for a party, rather than an individual. The parties themselves decide who goes on the candidate list for each of the 12 electoral regions. The ones at the top stand the best chance of being elected. The way seats are allocated within each European constituency uses the D'hondt system., which is a form of proportional representation.
What happened last time?
The last European elections were in 2009. The Conservatives got the biggest UK share of the vote, 27.7%, UKIP got 16.5%, Labour got 15.7%, the Lib Dems 13.7%, the Green Party 8.6% and the BNP 6.2%.
What about Scotland, Wales and Northern Ireland?
In 2009 in Scotland the SNP got 29.1% of votes, Labour 20.8%, Conservatives 16.8%, Liberal Democrats 11.5%, Greens 7.2% and UKIP 5.2%. In Wales, the stage is set for a fascinating contest. In 2009, four parties shared the spoils - with one MEP each for Labour, the Conservatives, UKIP, and Plaid Cymru. Northern Ireland is very different to the rest of the UK when it comes to the Euros. MEPs are elected using the Single Transferable Vote system - there are no party lists and you vote for a candidate by order of preference rather than a party. Ten candidates are vying for three seats.
And the smaller parties?
Smaller parties love the European elections because since 1999 it has used proportional representation. This year's crop of hopefuls include the English Democrats, which campaigns for English independence, and An Independence From Europe, founded by former UKIP MEP Mike Nattrass, both of which are running full slates of candidates. The Christian People's Alliance, and No2EU, a left-wing Eurosceptic party founded by the late RMT leader Bob Crow, are the next two largest parties, by numbers of candidates. But 30 parties in all are contesting seats across the UK.
A big day in London
Every seat in all 32 London boroughs - more than 1,800 in total - is up for grabs on Thursday, 22 May. This has not happened since the day of the general election in 2010, when Labour bucked the national trend by getting 36.4% of the vote to the Conservatives 34.5%. Ed Miliband's party lost to Boris Johnson in the 2012 mayoral contest. Mayoral elections are also taking place in Hackney, Lewisham, Newham, Tower Hamlets and Watford.
Elsewhere in this year's English local elections a third of seats are up for grabs in most councils.