The Beckhams have increased security at their home

The men had been charged with conspiring to kidnap the wife of England football captain David Beckham on or before 2 November last year.

But at a hearing at Middlesex Guildhall Crown Court, the judge was told the News of the World had paid £10,000 to a convicted criminal, Florim Gashi, for his story.

Prosecutor Brian Altman said: "Mr and Mrs Beckham have had explained to them the stance the prosecution feels compelled to take in this case and I am confident that they understand the reasons for taking these steps."

Adrian Pasareanu, 27, Alin Turcu, 18, Luzim Balliu, 30, and Joseph Rivas, 25, were cleared of conspiring to kidnap Mrs Beckham.

Two other men were also cleared but cannot be named.

No information was concealed or held back News of the World

Judge Simon Smith referred the News of the World's role in the matter to the Attorney General.

Last November the front page of the paper proclaimed "Posh kidnap - we stop £5m ransom gang".

Over several pages the paper's investigations editor Mazher Mahmood described how its reporters had infiltrated a plot to ambush Mrs Beckham.

The plotters had intended to demand a ransom from her husband, the paper said.

The judge said on Monday he was minded to refer the whole matter to the Attorney General "to consider the temptations that money being offered in return for stories concerning celebrities give rise to".

Bullish statement

The source of the story, Mr Gashi, was described as a Kosovan parking attendant who was in financial difficulties.

It was suggested in court Mr Gashi - who had a conviction for dishonesty - could have instigated the plot himself to make money from the newspaper.

But the newspaper was bullish in a statement, standing by its story and its tactics.

It said: "The News of the World is surprised by today's announcement. We fully stand by the report.

"The story resulted from a thorough and legitimate investigation undertaken by one of the paper's most senior and experienced reporters - a journalist responsible for more than 100 successful convictions.

"Since November we have co-operated fully with the police leading this inquiry passing on all evidence. No information was concealed or held back."

Media payments

The case is the latest to highlight the controversial issue of media payments to witnesses.

The Press Complaints Commission (PCC) and broadcasting regulators recently tightened up their codes of practice, following a government threat to make such payments illegal.

That followed the case of the schoolteacher Amy Gehring, during which schoolboy witnesses were offered money for interviews.

Newspaper payments also cast doubt on the credibility of evidence in the trials of Jeremy Thorpe, Rosemary West and Gary Glitter.

The rules say no payments may be made to a witness once proceedings have begun - and, before that, only if there is a public interest.

The News of the World would be expected to justify their actions. The payment was made before the proceedings started and one of the accepted "public interest" justifications is "detecting or exposing crime".

Sir Christopher Meyer, chairman of the PCC, said the trial's collapse raised "a number of significant issues relating to the administration of justice".

He added: "The rules on witness payments have in fact been considerably toughened since the News of the World broke this story.

"It is crucial that all publications adhere to these, and the PCC will certainly act in any case where a newspaper or magazine is found, after investigation, to have breached them."