Who will be voting in the referendum and how?

We look at some of the key battlegrounds as September 18 draws ever closer.

SENIOR CITIZENS: 860,000

While little is certain in the run-up to September 18, it is guaranteed that Scotland's 860,000 pensioners will vote in huge numbers.

It is a group the Yes campaign has so far struggled to win over, with the Better Together campaign capitalising on concerns over security of pensions in an independent Scotland.

David Ness, a sociologist at the University of the Highlands & Islands, said: "Older people are more likely to have a strong sense of British identity."

NON-SCOTS: 400,000

Polling suggests around two-thirds of English voters resident in Scotland plan to back the UK.

"It is not altogether surprising - they would after all be voting to become what some may consider a foreigner in your chosen homeland" said Dr Neil McGarvey, a politics expert at the University of Strathclyde.

UNDER-18s: 125,000

For the first time, 16 and 17-year-olds will be given a vote. Around 125,000 teenagers, who under normal election rules would have been excluded, can vote.

Dr Jan Eichhorn, of the University of Edinburgh's School of Social and Political Science, said: "You have very few political geeks but that's the same as the adult population. We're confident there will be a high turnout, with 80 per cent registered."

MILITARY: 15,000

Few groups have more at stake. Scottish members of the armed forces, in the event of a Yes vote, would be faced with the choice of joining a new Scottish defence force, eventually rising to 15,000 regular and 5,000 reserve personnel. Dr McGarvey says: "The anti-nuclear agenda of the Yes campaign does not sit easily with many in Britain's armed forces."

UNEMPLOYED/DISENFRANCHISED: 190,000

If voter registration drives and canvassing succeed, it will increase turnout in a group that is more likely to want change - and therefore far more favourable to the Yes cause. Dr McGarvey said: "Voting against the status quo is likely to be more attractive to those with least to lose. Generally speaking the lower your income - and the more economically and politically marginalised you feel - the more likely you are to vote Yes."

MEN OF WORKING AGE: 1.65 million

Polls have consistently shown that men are more likely to back a Yes vote.

And with 1.65m males aged between 18 and 64, they will prove one of the two most important groups for the campaigns to win over.

WOMEN OF WORKING AGE: 1.7 million

The referendum may well be won or lost here.

Emily Thomson, co-director of Glasgow Caledonian University's Women in Scotland's Economy Research Centre, said: "Women's employment patterns may reflect difficulties in accessing affordable childcare which impacts negatively on their earnings and labour market prospects." she said.