The investigation was launched on 19 August, after a Freedom of Information request disclosed that a number of individuals depicted in the leaflet were stock photos, and their stories were fictional, albeit "based on conversations our staff have had with claimants", the DWP said at the time.
The institute investigated this case of 'astroturfing' – falsely creating the impression of independent, popular support – on the grounds that such practices contravene its Code of Conduct due to a lack of honesty and integrity, and that they bring the profession into disrepute.
In early September, the CIPR agreed to suspend its investigation following confirmation that the DWP was conducting its own investigation.
In a statement published on Friday, the CIPR said it had now been confirmed by the DWP that no members of the institute were involved in or responsible for the leaflet. The CIPR's investigation has therefore been closed.
The CIPR said it had been told by the Government Communications Service that government comms professionals "continue to be advised of expected standards of best practice in line with the Civil Service Code".
Sarah Pinch, president of the CIPR, said: "Honest regard for the public interest; delivering reliable and accurate information; and a commitment to never knowingly mislead are vital components of proper professional practice – and I am pleased that in this case, the DWP and GCS have confirmed that no members of the institute were involved.
"This is an opportunity to remind members of the CIPR that they are publicly accountable for the standard of their professional conduct, and the conduct of those under their management. This accountability is a valuable asset not just to members themselves, but also to the public, to clients and to those who employ them."
The DWP was not immediately able to confirm the progress of its internal investigation.