The ethics committee have written to all bidding nations - England are among those - telling them to "respect fair play".

The rules of conduct laid down by FIFA are not as stringent as the IOC's for Olympic bids but still outlaw financial 'gifts'.

They also prohibit any bidding nation doing a deal with another - for example England agreeing to back the USA for 2022 in return for support for their 2018 campaign.

Claudio Sulser, a former Swiss international player who became a lawyer, has been appointed the new chairman of the FIFA ethics committee - previous chairman Sebastian Coe stepped down to become part of England's bid.

FIFA said in a statement: "The committee agreed to send a letter to all of the member associations bidding for the 2018 and 2022 FIFA World Cups in order to remind them that they have signed regulations to respect fair play in this contest and that the ethics committee will remain vigilant to ensure that all regulations are adhered to."

FIFA president Sepp Blatter added: "Football has reached a huge economic dimension. All of this brings not only a social responsibility, but a moral commitment too. This is why it is so important to have an independent ethics committee that can supervise and make sure that fair play and the code of ethics are respected."

Sulser, who is also a member of the Olympic anti-doping committee, said he was honoured to chair the committee.

"I am certain that we can do something positive if we work together as a team, with a transparent approach and with a clear application of the code of ethics in order to protect the integrity of football," said Sulser.