Four England rugby players allegedly involved in a sex assault in New Zealand have been told they can leave the country with the rest of the team.

Police say the players, who deny any wrongdoing, are free to go, because the woman said to be involved has not made a formal complaint.

An incident is alleged to have taken place on Sunday night in the team's hotel after England's 37-20 defeat by the All Blacks.

Police confirmed the allegation is one of rape or serious sexual assault and confirmed the unnamed players had declined to be interviewed by officers after taking legal advice.

Rugby Football Union (RFU) chief executive Francis Baron said the players were "desperate" to clear their names but felt unable to do so.

Mr Baron said the players were "upset and very frustrated".

He said: "The police have mentioned, through our legal representatives, four names. Each of the individuals has denied any wrongdoing in the strongest terms.

"There are some lurid allegations floating around. The boys have totally denied them. In our view, those boys are innocent until proven otherwise.

"I know the boys are very upset and very frustrated they can't clear their names as soon as possible."

Auckland City Police said in a statement: "Members of Auckland City Police's adult sexual assault team flew to Christchurch in the hope of being able to speak with the four England rugby team players at the centre of a serious sexual assault allegation.

"The players have advised police - via legal representation - that they are declining to be interviewed by police on the matter at this stage.

"Auckland City Police will continue to investigate the allegation - that a woman was raped and/or sexually assaulted by four players - as thoroughly as possible before reviewing the file."

The statement went on: "Any decision about where to take matters from there will depend on the outcome of that review.

"While no formal statement has been made by the woman who made the allegations, a formal complaint can be made at any time in the future and police are then obliged to assess the evidential basis of that complaint."

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