Image copyright Thinkstock

Millions of people will head to polling stations across the country on Thursday to mark their chosen box with that all-important cross. But who are the people who will not vote?

Can't vote

Image copyright PA Image caption MPs voted in favour of lowering the voting age to 16 in 2013 but the law was never changed

Under 18s

The voting age was lowered from 21 to 18 in 1969 and in recent years efforts have been made to allow the UK's two million 16 to 18 year olds to participate.

In 2013 a backbench motion calling for the change was passed by the Commons by 119 to 46, a majority of 73, but the result was not binding and the law was never changed.

Liberal Democrat politician Stephen Williams, who has championed the cause, said lowering the voting age would drive up turnout among young people and lead to greater political prominence for issues affecting them.

He said: "Over the last 15 years that I've been an MP and prospective parliamentary candidate I've spoken to schools, sixth forms and further education colleges on many occasions and I've always been impressed by the questions and range of interests that 16 and 17 year olds show in politics.

"You can do so many other things at 16 including the most fundamental thing anyone can to have a relationship with somebody and to bring a child into the world.

"To not allow them to vote is pretty well indefensible.

"When people say they are not sure 16 and 17 year olds know enough about voting I dispute that. We do not apply that test to anyone who is older. I've met people in their 50s and 60s who do not know much about politics.

"If the voting age was reduced they would become even better prepared for voting."

The Labour Party has pledged to lower the voting age to 16 by May 2016 while the Liberal Democrats said they would make the 2020 general election open to 16 to 17 year olds.

The Green Party also wants to introduce the right to vote at 16.

Members of the House of Lords

Image copyright Getty Images Image caption Lord Scriven said the bar on peers voting in general elections should be scrapped

Members of the House of Lords have for hundreds of years been barred from casting their vote in general elections, though they are able to vote in local and European elections.

A spokesman for the House of Lords said: "This has been the practice for many centuries. The reason for this, it is thought, is that as members of Parliament they can represent their own views in Parliament so they should not have a second opportunity to have those views represented in Parliament by electing someone to do so in the House of Commons."

For Lord Scriven, the former leader of Sheffield City Council who stood in the 2010 general election, 7 May will be the first time he has not voted at a general election having been appointed as a Liberal Democrat life peer in 2014.

"It's rather surreal really," he said.

"Nothing else changes, you are still fighting for your party, you still hold the same values and beliefs yet, at the critical moment, you won't be able to cast a vote to elect your MP.

"You kind of have your hands tied behind your back and your mouth taped and you are not able to have your say.

"I've been living and breathing politics since my teenage years and it's the first time ever I'll be choosing who I wish to represent me in my constituency or having a say on who I would like to see in government."

Lord Scriven believes that the ban on voting should be removed, describing it as "quite quaint and archaic".

He said: "I went in knowing the rules meant I would not have my vote but it seems much more real now.

"I think the law on Lords not having a vote was set a long time ago. Many ordinary people now sit in the Lords and I think ultimately we should be given a voice."

Since the Parliament Act was passed in 1911, MPs have been able to override any decision made in the Lords, effectively giving it a subordinate role in the legislative process.

Prisoners (apart from remand prisoners)

Image caption More than 70,000 prisoners will be unable to vote in the general election

According to the Representation of the People Act 1983: "A convicted person during the time that he is detained in a penal institution in pursuance of his sentence …is legally incapable of voting at any parliamentary or local election."

The Howard League for Penal Reform says there are more than 85,000 people currently in jail in the UK, of which about 12,000 are on remand.

In 2005 the European Court of Human rights ruled that the UK's blanket ban on prisoners voting must be amended.

However to date no change has been made to the law despite a draft bill, proposing options to allow them a vote or retain the status quo, having been drawn up in 2012.

Juliet Lyon, director of the Prison Reform Trust, which has campaigned for prisoners to be allowed to vote, said: "People are sent to prison to lose their liberty; not their identity.

"The 19th Century punishment of civic death makes no sense in a 21st Century prison system focussed on effective rehabilitation.

"The UK is out of step with most European countries, as well as many states around the world.

"Even the modest proposals made by the cross-party committee set up to consider the draft prisoners voting bill have fallen on deaf ears."

UKIP has set out in its manifesto that prisoners will not be allowed the vote while the Conservatives say they will scrap the Human Rights Act, and introduce a British Bill of Rights in order to break the link between British courts and the European Court of Human Rights and "make our own Supreme Court the ultimate arbiter of human rights matters in the UK".

Don't vote

Image caption Jehovah's Witnesses are among those who do not vote based on their religious beliefs

Jehovah's Witnesses

There are about 140,000 Jehovah's Witnesses in the UK who will choose not to vote on 7 May.

Mark O'Malley, a spokesman for the Christian-based religious movement, said: "As you go through the bible we see that God's kingdom is already established in heaven with God as the king of that kingdom.

"We are politically neutral as, in a sense, we have already chosen to support that kingdom's government. We see it as a real government.

"There are limitations to what governments can do, maybe they can improve the health system, but they can't prevent death, maybe they can help children, but they can't provide a secure future for them necessarily. Only God's government is going to be able to resolve completely the real, deeper issues."

Despite their choice to opt out of voting, Mr O'Malley said Jehovah's Witnesses were "model citizens", living their lives by principles set out in the bible which states "authorities that exist have been established by God" and to rebel against them is to rebel "against what God has instituted".

He said: "We take the Bible principle at Romans chapter 13 which tells us to support the superior authority.

"The bible highlights respect for government, respect of authority, respect for civil laws so you will see Jehovah's Witnesses are model citizens when it comes to paying taxes and working within the laws created by government because that's something that is engendered in the pages of the bible."

Similarly, Christadelphians choose not to vote, saying: "[Leaders] will come and go. But there will be no lasting peace or happiness for the world until the reign of Jesus, the ideal leader, chosen and prepared by God."

Image copyright WPA Pool Image caption Royals are not banned from voting but it is considered "unconstitutional" for them to do so

The Royal family

According to the official website of the British Monarchy the Queen and her family "never vote or stand for election to any position, political or otherwise".

It says that although the law does not ban royalty from voting it is "considered unconstitutional for the Sovereign and his or her heir to do so".

"As Head of State, The Queen must remain politically neutral, since her government will be formed from whichever party can command a majority in the House of Commons.

"The Queen herself is part of the legislature and technically she cannot therefore vote for members of another part of the legislature."