As millions of Britons turn out to vote, the two major parties remain neck-and-neck in the opinion polls in what experts are dubbing the most unpredictable general election in decades.

On Thursday it was predicted Britain could be heading for a hung parliament, with the polls indicating neither the Conservative Party nor Opposition Labour Party would win enough seats for an outright majority in the 650-seat parliament.

“This race is going to be the closest we have ever seen,” Labour Party Leader Ed Miliband told supporters in Pendle, in northern England, on the eve of the vote.

• CLICK HERE FOR ELECTION RESULT
• Best and worst front pages of the UK election
• MP declines sword fight duel

“It is going to go down to the wire.”

British Prime Minister David Cameron said only his Conservatives could deliver strong, stable government and “all other options will end in chaos”.

Of seven opinion polls released on the last day before voting, three showed the two main parties tied.

Another three put the Conservatives ahead by a single percentage point, and one gave Labour a two-point lead.

Leading pollster Peter Kellner of YouGov predicted the Conservatives would end up with 284 seats to Labour’s 263, with the Scottish Nationalists on 48, Liberal Democrats 31, the anti-European Union UK Independence Party (UKIP) two, Greens one, and Welsh and Northern Irish parties 21.

If that proved correct, either of the two big parties would need support from at least two smaller ones in order to get laws through parliament.

Polls opened at 7am (4pm AEST).

Around 50 million Britons are eligible to vote at polling stations located everywhere from shipping containers to churches and pubs on the mainland and remote islands that will close at 10pm (0700 AEST Friday).

Voter confusion

While five years of reduced spending under Mr Cameron had slashed Britain’s budget deficit and reduced the unemployment rate to its lowest since 2008, many voters felt the growth hadn’t been made its way into their back pockets.

Residents wait to cast their votes at a polling station in Elvetham Heath in southern England. Photo: Getty

Which begs the question as to why Mr Cameron’s Conservatives are on a knife-edge with Mr Miliband’s Labour Party, with neither expected to win an outright majority.

Amid at least a dozen cranes at work on the edge of the City of London, raising edifices bearing the names “The Eagle” or “The Atlas”, the disconnect had turned many voters undecided just a day before polls open, The Christian Science Monitor reported.

“They are building all these massive flats, but it masks the marginalisation of the city,” a young NGO worker at the Old Street underground station Sania Sajid told The Christian Science Monitor.

The Old Street area was rundown just a few years ago, but is now seeing a major facelift as start-ups move in and old buildings are replaced with new offices.

Ms Sajid commended Mr Cameron’s economic track record but said she didn’t know which party she would cast her ballot.

“The social and economic gap has increased. There is a real underbelly in London of people who can’t cope,” she said.

#PollingDay in #ukelection2015. Polling from 7am to 10pm. Do vote. It’s our right that secures our future!

— loveena tandon (@loveenatandon) May 7, 2015

This election reveals how the UK, once a dominant player on the world stage, is turning inward #ukelection2015 http://t.co/MQTlgf7V75

— NewsFlow (@theeurodaily) May 7, 2015

Excited to #VOTE in the #ukelection2015 today. Hundreds of #women fought for this right & I fully intend 2do them proud. #feminism #equality

— L Miller (@TheLooseE) May 7, 2015

We have a vote in this country so make sure you use it wisely. #ElectionDay #ukelection2015 pic.twitter.com/QHeaOR4uGv

— Warren Holt (@wjwholt) May 7, 2015

The only reason I would ever vote #UKIP is if they were a party promoting afternoon naps #GE2015 #ukelection2015 #election2015

— Gemma Ferguson ✨ (@x_gemski) May 7, 2015

– with agencies