Foreign sportsmen and women, and other foreign staff taking part in the London 2012 Olympic and Paralympic Games, have been exempted from income tax.
The change was first agreed in principle in the 2006 Budget but has now been enacted by Treasury ministers.
The exemption from income tax and corporation tax was a condition of London being awarded the games.
HM Revenue & Customs (HMRC) said the arrangement would only benefit a few people.
"For most people working at or supplying to London 2012, there will be no specific tax exemptions in place, and normal tax laws apply," HMRC said.
"There are tax exemptions available for a small number of non-residents who are directly involved in the delivery of the games."
People associated with the games can only benefit from the tax exemptions so long as they are "neither resident nor ordinarily resident" in the UK in the 2012-13 financial year.
The income or payments that will avoid tax must also be "wholly and exclusively" for taking part in the games.
The exemption from income tax lasts from 30 March 2012 to 8 November 2012 and covers:
- media workers such as journalists
- representatives of official Olympic bodies such as the IOC and foreign governments as well as host cities for future games
- equipment technicians for the games
- team officials
- and technical officials such as judges and referees.
Officially designated Olympic partners, who provide a commercial service to the games, have been given a similar tax exemption.
Staff who work as employees or contractors for Olympic broadcasters will also be covered, but for a longer period - from 6 April 2011 to 5 April 2013.
Performers at the official opening and closing ceremonies will not pay tax either on payments for their performances and rehearsals.
The London Organising Committee was exempted from corporation tax by the 2006 Budget.
The Olympic tax regulations were laid before Parliament last week, and come into force on 1 January 2011.