Doping offenders at the Beijing Olympics will be banned from the next Games in London 2012, says the International Olympic Committee (IOC).

The IOC formally ratified the new rule which will be voted on in a meeting in Beijing, though the change does not affect participation at the 2008 Games.

It means any athlete who is banned for six months or more for a doping offence will be banned from the next Olympics.

It will come into force on 1 July and will affect any offenders at Beijing.

"Should an athlete get caught doping in Beijing and then get a sanction of six months, he or she will not be eligible for the 2012 London Games," said IOC communications director Giselle Davies.

All major doping offences including blood doping and steroid use usually carry a two-year suspension for first-time offenders.

The IOC initially said it would need a charter change to introduce it and so could only come into force after the Beijing Olympics, where the IOC will meet.

But the rule was labelled an eligibility rule that could be approved by the Executive Board without a charter change and be brought forward to include Beijing.

Drugs testers will perform some 4,500 doping tests during the 8-24 August Games, up from about 3,600 in Athens four years ago.

Athletes can be tested more than once on the same day and all top five finishers as well as two other random athletes will also face tests.

There will be a total of 41 doping control stations, 34 in Beijing and seven in the co-host cities where some other sports will be staged.

British sprinter Dwain Chambers is due to challenge his British Olympic Association ban from the Beijing Games next week.

Meanwhile, the IOC plan to clamp down on gambling corruption by setting up a new unit at this summer's competition.

The unit will monitor "abnormal" betting patterns during the Games.

"We have signed an agreement with the major bona fide betting companies and we will rely on them to advise us if there is an abnormal pattern of betting or something suspicious," said IOC chief Jacques Rogge.

"There may be legitimate reasons why there is a surge in betting but it's clear we need this collaboration."