It is Christmas 1914 and World War One has been raging for several months. On the Western Front, trench warfare continues to take the lives of thousands of young men. But for one day the soldiers stop fighting and engage in a familiar ritual; one that is loved by soldiers on both sides - England versus Germany at football.

Football is undoubtedly the world's primary sport. Played across the globe, from Brazilian beaches and African shantytowns to the great European arenas, football brings people together. Millions of us descend on stadiums, bars and living rooms every weekend to watch our teams play. Old women curse, children cheer and people from completely different walks of life are brought together, just like the English and German soldiers.

However, for all the romance, it has to be recognised that football is also big business. And, just like with textiles or food, as consumers we should buy ethical. When choosing a club to support, fans can help stop corrupt and unsavoury characters profiting from their beloved sport.

While it is traditional to follow one's local team, the availability of games and information on television and the Internet has led many fans to follow one of Europe's elite clubs. Even amongst this small group though, there is an important ethical decision to be made.

The most popular league in world football is the English Premiership. This season, big spenders Manchester City and Chelsea are expected to challenge Manchester United for the title. Both clubs have grown rapidly since being taken over by billionaire tycoons. Both clubs are also now examples of immoral men using the world's most popular sport to further inflate their wealth, power and egos.

In June 2003, Russian oligarch Roman Abramovich bought Chelsea. Eleven years earlier he was arrested for stealing Government property (a train containing 55 tankers of diesel fuel.) In 1995, he acquired his oil company, Sibneft, with Boris Berezovsky. Berezovsky is now wanted in Russia on charges of corruption.

In court papers obtained by The Times, Abramovich admits that he used bribes to secure Sibneft for a tiny fraction of its market price. He also admits that he paid for protection from gangsters during the infamous "aluminium wars", in which Abramovich emerged victorious, following the murders of plant managers, metal traders and journalists. The court papers themselves were the result of Berezovsky suing Abramovich for blackmailing him.

If there is one thing that is clear about Abramovich's murky past it is that he and his fellow oligarchs have profited massively at the expense of millions of Russians who remain so stricken by poverty that many long for a return of communism.

Another billionaire who profits at the expense of his fellow countrymen is Sheikh Mansour, a member of the royal family that rule the United Arab Emirates. He is Minister of Presidential Affairs and the half brother of the President. Mansour is part of a regime with an atrocious human rights record, marred by the unfair treatment of women, homosexuals and expatriate workers, thousands of whom have been coerced into moving to the region, trapped and forced to live as debt ridden, de facto slaves.

One of Mansour's half brothers, also a Sheikh or "Prince", was caught on tape last year "setting fire to and running over a helpless Afghan he had accused of cheating him in a business deal". He will not be punished.

Since September 2008 Mansour has had another job. He is the owner of Manchester City who, thanks to the hundreds of millions of pounds of dirty money he has invested, will now compete with Abramovich's Chelsea for the Premiership title.

Any football fan with a sense of justice must surely be troubled by the notion of supporting Manchester City or Chelsea, given that it means supporting the status and bank balance of Sheikh Mansour or Roman Abramovich. Indeed, there are a number of clubs that fans concerned about the ethical implications of their support should avoid.

However, there are also many other clubs that need not weigh on the conscience of their fans. Take Barcelona, European champions, possibly the greatest team of all time and certainly the best team in the world today. The club's rich history and importance to Catalan culture is embodied in its motto, "Mes que un club" (more than a club in English).

Barcelona is owned by 170,000 of its supporters and is run by an elected President. Until this season, it rejected shirt sponsorship, instead displaying the charity Unicef on its famous striped kit.

Barcelona emphasises the development of players from a young age at its La Masia academy and the majority of the current squad have been at the club since they were children. Its three star players - Xavi, Iniesta and Messi - are all La Masia graduates. As well as playing some of the most mesmerising football ever seen, they act as role models off the field, with their professional attitudes and relatively modest lifestyles.

I for one hope that clubs like Barcelona continue to succeed in preserving everything that is good about football. We should help such clubs by supporting them and rejecting the dirtying of the beautiful game by the likes of Abramovich and Mansour.