The contest to be the BBC's Sports Personality of the Year for 2012 is poised to be the closest in history as Britain's sporting heroes of an incredible year go head to head for one last time.

The winner from the shortlist of 12 - five women and seven men - will be decided by public vote but after a remarkable year for British sport any predictions must carry a health warning.

Tour de France winner Bradley Wiggins, who also won an Olympic cycling gold, has long been the bookmakers' favourite but there have been signs this week that he faces a real challenge from Olympic athletics champions Mo Farah and Jessica Ennis.

A poll of 2,000 people carried out for Coral bookmakers rated Farah's 5,000 metres and 10,000m triumphs ahead of Wiggins' exploits as the greatest individual sporting performance of the year.

The survey found just over 25 per cent of people thought Wiggins, the first British cyclist ever to win the Tour de France, would receive the BBC award with Farah on his shoulder at 23.45 per cent and heptathlon champion Ennis named by 19.65 per cent.

Ennis, the 26-year-old from Sheffield, has finished in third place twice before and believes nothing can be predicted.

She told the Press Association: "I'm not even thinking about it to be honest. There's so many factors flying around that it's so hard to call it, especially this year where everyone has done so well.

"Just look at the list - everyone has achieved just about as much as they possibly could have."

Other candidates in contention include Andy Murray, who not only became the first British man to win a grand slam tennis title in 76 years at the US Open but also took Olympic singles gold and mixed doubles silver.

Lymington-based Ben Ainslie, who made it four golds at successive Olympics to go with a silver in his very first Games in 1996, became the world's most successful sailor. In any other year Ainslie would stroll it to the award but he has no expectations.

He said: "I'm going to be really relaxed as I don't hold out any hope of winning anything. I'm sure it will be a great atmosphere and a final occasion to celebrate for one last time the amazing achievements - and then move on with the rest of our lives."

Ennis is something of a torchbearer for sportswomen in this year's BBC awards, especially after last year's controversial shortlist which saw not a single woman nominated. Olympic rowing champion Kath Grainger, Nicola Adams - the first ever women's Olympic boxing champion - plus Paralympic swimmer Ellie Simmonds and cyclist Sarah Storey join Ennis on the 2012 shortlist.

Ennis added: "I think after the disappointment of last year of not seeing a single female in the top 10, what British women have done in sport this year has been amazing.

"To have five women on the shortlist is incredible but it's fully deserved."

The only nominee who did not compete at the Olympics or Paralympics was golfer Rory McIlroy, who secured a stunning eight-shot victory at the USPGA Championship and who also featured in Europe's Ryder Cup comeback victory over the United States.

David Weir, the wheelchair racer nicknamed 'Weirwolf', has attracted significant backing for his achievements in winning a clean sweep of four gold medals at the Paralympics.

The shortlist contains one former winner too - Sir Chris Hoy, who won the award in 2008 after the Beijing Olympics and whose two cycling titles in London gave the Scot a British record six Olympic golds - one more than rower Sir Steve Redgrave.

Other awards on Sunday night will be chosen by panels for the team of the year, overseas personality, coach, young sports personality, the 'Unsung Hero', a lifetime achievement and the Helen Rollason award.