By David Martin, PA Sport, Berlin

IAAF general secretary Pierre Weiss hopes Dwain Chambers does not win the 100 metres at this summer's World Championships in Berlin.

The controversial British sprinter has publicly voiced his intention to defeat Olympic sprint champion and world record holder Usain Bolt this season.

The sport's governing body on Saturday confirmed they would not be taking any action against Chambers over his book, 'Race Against Me', in which he details the drug use that saw him banned from the sport in 2004.

But the IAAF's goodwill towards Chambers, which included sanctioning his return to competition even though he had not repaid prize money he earned during the period he cheated, has its limitations.

"In my opinion, the winner in Berlin should not have been a dirty athlete in his life," Weiss said.

Lord Sebastian Coe, an IAAF vice-president, also voiced an opinion that "you have to hold your nose" when drug cheats such as Chambers are allowed, under current regulations, to resume their careers.

When asked whether he thought Chambers was clean when winning his recent European indoor 60m title, Coe said: "I have to assume, and I have to assume for the very simple reason that you can only presume we are in a sport of total liability, and we can only assume guilt from a positive test.

"I have my own emotional moments about drugs in sport but I do also have to remember that the burden of proof can only be in a positive test."

Coe added: "If you're saying to me am I ever going to be comfortable about seeing somebody who I know has cheated coming back into my sport, the answer is no, I can't be.

"I also recognise there is a practicality about what I am saying and that, if you have a sanction and that sanction isn't a life ban, then you actually sometimes have to hold your nose and accept that people within the laws of the sport come back."

Chambers' book is the latest......