The BBC Trust found that, although Lord McAlpine denied the allegations when he was contacted by a Channel 4 News journalist before Newsnight was broadcast, the BBC still made no attempt to contact the peer, which it should have done.
Trustees also said that concerns had been raised previously about the credibility of some of Mr Messham's evidence - which was known to members of BBC Wales, but no effort was made to contact them.
The Trustees considered that parts of BBC News not contacting colleagues in the nations and regions when investigating stories on their patch was very poor practice.
More top news
The forecast is generally calm, quiet and dry as an area of cloud gives way to the south east and moves off to the near continent.
Artists have retold the stories of "imponderable brutality and evil" in works created to remember the Holocaust.
ITV News joins 85-year-old Holocaust survivor Zigi Shipper on his emotional return to the Auschwitz death camp.