Memorial: Flowers laid at the scene of the accident

The prosecution at Swansea Crown Court offered no evidence after making submissions to the judge at the start of the trial on Tuesday.

Formal verdicts of not guilty were entered for both Railtrack and the CCW who will have their costs paid by central funds.

Following the collapse of the case, HM Inspector of Railways, Chris Carr, said: "We regret having found it necessary to withdraw the prosecution against Railtrack and CCW.

"The prosecution is obliged to keep its evidence under review during a prosecution. In this case new information came to light that prompted the HSE to evaluate its ability to continue.

The track on which the girls had been playing

"The prosecution was commenced after proper application but the situation under which the initial review was made consequently changed.

"Railtrack and CCW do have a clear duty imposed on them by HSE legislation to ensure that the safety of the general public is not compromised.

"We are therefore pleased to note that the footpath involved in this case has now been adequately fenced, stile removed and access to the railway line by that method has been prevented."

A spokesman for Railtrack said the company had no comment to make.

In July 2001, Sophie's mother and stepfather, Amanda and Gareth Edwards, were found guilty of manslaughter after allowing the children to play on the railway during a picnic.

They were given a 12-month prison sentence, suspended for 12 months, in a court case in Swansea.

Amanda Edwards was convicted last year

Following the result of the earlier trial, Tony Allcock - Kymberley's father - said he intended to take the case to the European courts and would consider a private prosecution.

The case against Railtrack and the CCW had been launched for alleged breaches of health and safety rules.

Both organisations had denied the allegations.

A memorial to the two schoolgirls has been unveiled close to the scene of the tragedy.

The youngsters were killed by a train while playing unsupervised on the railway bridge.

They had been taken on a picnic by Mr and Mrs Edwards with the girls' two brothers and the couple's young babies.