IT will never be known what caused thousands of postal ballot papers to go missing at the local and Euro-elections, council chiefs have revealed.

A report into what went wrong has failed to establish a definitive answer to why an estimated 6,000 voters failed to receive their postal voting packs before this year's Bolton Council elections.

But council bosses and Royal Mail chiefs today continued to blame each other for the fiasco.

Emergency polling stations had to be set up in the borough just hours before the close of the ballot in June as thousands of voters revealed they had not received their packs.

The report revealed by council chiefs today raised questions over the performance of the Royal Mail, in particular as to why it charged the council for delivering all 191,976 ballot papers - one for every voter - if it had not received all the voting packs from the council.

At the height of the furore over missing voting packs, the Royal Mail claimed it had delivered everything it had been given by the council.

The report claims that even at this stage voting packs continued to arrive through the post.

But Tory councillors have dismissed the report as a "whitewash".

Returning officer Bernard Knight said: "We will never know the complete answer as to what went wrong.

"But it is clear that there was a problem at the Royal Mail. They were delivering ballot papers right up until the last day of voting after earlier claiming that everything had been sent out.

"I am sure they were telling the truth but I believe bags ended up in other parts of the country and were only delivered when they were returned to sorting offices."

The report concludes: "The unfortunate fact is that because of a lack of a clear audit trail, a wholly accurate answer to what went wrong in Bolton will not emerge". But it also reveals that a Royal Mail liaison officer had admitted to council officers Bolton ballot packs had been discovered in a sorting office in Oldham -- but that this was never proved.

The reports continues to claim that council chiefs have receipts showing that all ballot papers were with the Royal Mail by Friday, May 28 -- four days after the Government's deadline.

It says the delay was caused by nearly 30,000 errors being spotted in town hall checks on ballot packs received from printers Thomas Dornan, of Oldham, before they were handed to the Royal Mail to be sent out.

A spokesman for the Royal Mail said this delay had caused "problems".

But she added: "We have seen no evidence from Bolton that we were at fault, so we cannot at this point comment further."

Cllr Andy Morgan, the Conservative group whip, described the report as a "whitewash".

He said: "People out there are going to be asking what went wrong and we cannot tell them.

"This report has achieved nothing but now is the time to move on and make sure nothing like this ever happens again."

But leader of the council, Cllr Barbara Ronson, said election staff had done everything possible to investigate what went wrong.

She said: "Once it was realised that there were problems, our staff did everything they could to make sure people got their votes and to get to the bottom of what went wrong."

Deputy Labour leader Linda Thomas said: "The Royal Mail seems not to acknowledge the problems when in some areas it was obvious people had not received their postal votes.

"Although voting did go up, perhaps we should accept that we are not quite ready as a town to accept the responsibility of postal voting."