An investigation into how submissions over the Northern Distributor Road went 'missing' has failed to arrive at a definitive view as to what happened.

The Norfolk County Council probe was launched after complaints by The Green Party, campaign group Stop Norwich Urbanisation (SNUB) and the Campaign to Protect Rural England, that their submissions over the road were lost.

They all made representations to the county council over the road and said they had received automated email responses to prove it.

But they said their submissions were not part of the county's consultation files which have been submitted to the planning inspectorate - ahead of this summer's inquiry into whether the £148.5m road should get permission.

Their complaint led to an internal investigation at County Hall, conducted by Al Collier, head of procurement.

His report was published today, in which he concluded he was 'unable to arrive at a definitive view as to what happened', but that he believed the council had received the submissions.

He said: 'I find the alternative – that receipts were 'spoofed' by the complainants or that the complainants submitted emails which they then managed to recall without the council's knowledge – far-fetched.'

But he said it was unlikely the emails were logged by the team working on the Northern Distributor Road, which was tasked with manually logging and filing each one.

He said: 'The print logs show they were never printed by the logging officers. Printing normally took place at or shortly after the point of logging.

'To 'invisibly' remove a submission from the spreadsheet log would have required amendment also of paper files and electronic records.

'Because the logs, the paper files and the electronic records were sequentially numbered, this would have required significant effort and risk of detection.

'Anyone amending the record would have had to renumber each email received after the deleted email in the spreadsheet; copy the emails back into the mailbox in order to change the email title; save the emails under a different name; and print new paper copies and insert them in the file.'

Mr Collier suggested that one or more of the emails may have been 'put aside to be dealt with later' because of their complexity, but then got mislaid.

But he said it was 'implausible' that the NDR team deleted one or more emails in order to somehow improve the prospects of the road being approved.'

He said the apparent lack of a submission, particularly by the Green Party and SNUB had been noted by some middle managers, but they did not think it was up to the council to contact them to ask why.

Mr Collier's report said there were clearly 'problems' with the process, but that the planning inspectorate had concluded the complainants had not been prejudiced by the omissions as the themes of objections had been raised by others.

Council bosses said steps would be taken to prevent such losses happening again.

Tom McCabe, interim director of environment, transport and development at Norfolk County Council, said: 'I am sorry that it has not proved possible to find out why the three emailed submissions went missing, but it certainly should not have happened and we are taking immediate steps to make sure that it does not happen again.

'The county council's head of procurement has carried out an extremely thorough investigation, and although he has not been able to pin down the reasons, we have apologised to the Green Party, SNUB and CPRE.

'The county council is committed to a full and open examination of the NDR application and it was in nobody's interests for this to happen.

'It is important that the Planning Inspectorate has concluded that none of the three organisations has been disadvantaged.

'We accept the report's recommendations that in future the council should whenever possible use a web-based consultation system, and build in additional safeguards where email is still used.

'We are also looking at improving staff training, and a review of log retention policies to allow for investigation if things do go wrong in future.'

But the campaigners whose submissions went missing said questions still needed to be answered.

A statement issued on behalf of CPRE Norfolk, SNUB and Norwich Green Party, said: 'This is an extremely disappointing but frankly not surprising outcome.

'Despite all their efforts the council cannot explain how the objections of three major opposition groups, representing tens of thousands of people, went missing. But we are somehow just supposed to accept it as 'one of those things'.

'There are two possible conclusions we can draw from this, both of which require further action.

'If they were deliberately deleted by someone, then further investigation needs to be taken by Norfolk County Council or others to determine who this was; including re-interviewing all staff members, current ones and those who have left the council, who had access to that particular email inbox.

'But If it was a technical or accidental error, then it is so statistically unlikely that it was just our three submissions went missing, as to be unbelievable.

'In which case we must presume, that if this 'error' happened to us, it could have happened to other responses, and this possibility has not been fully explored.

'It is not unreasonable to assume that many other responses could have been accidentally deleted, which has significant implications on the validity of their consultation process.'

The inquiry over the NDR, which would stretch from the A47 at Postwick to the A1067 at Fakenham Road, is due to take place this summer.