Agency staff and in-house Royal Mail casual workers are being blamed for a catalogue of errors in the postal service.

A Channel 4 Dispatches programme, screened last month, claimed to expose widespread fraud, theft and incompetence within the postal service. Untrained agency workers were held partly responsible for the malaise.

However, Norman Candy, postal executive member for London for the Communication Workers Union, said the real problem lay in Royal Mail’s improper use of the workers.

“We recognise that there are times when short-term staff is the appropriate solution to the problem,” he said.

“What we object to is the fact that Royal Mail appears to be using temporary staff as a permanent solution, even more so when most of these people are not properly trained and most of them are not trained at all. Agency [and casual] staff are being used by the Royal Mail inappropriately.”

Two agencies – Manpower and Reed Employment – supply staff to the Royal Mail, although the Royal Mail uses other agencies if the two cannot find suitable people.

Manpower denied that any of its workers were involved in the allegations made by the programme. A spokesperson said: “The bulk of the staff that we provide to the Royal Mail is on its driving side. Sorting and delivering the mail is not an area that Manpower gets involved in.”

A spokesperson for the Royal Mail said: “The Royal Mail is undergoing a review at board level of its practices and procedures in its letters business. There will be particular focus on the recruitment, security, vetting and training of temporary staff.”

Reed declined to comment.