More than 1,000 unidentified bodies found across England and Wales over the past 50 years could be named as a result of a sweeping cold case review.
Police said they want to "put an end to the story" for many families left bereft by the disappearance of loved ones who have never been traced.
Officers have launched a £50,000 review using the latest forensic techniques and public appeals aimed at putting names on the files of non-suspicious deaths.
Officers released sketches of the faces of 18 men and two women found dead on the railways and London Tube network to mark the first stage of the operation today.
They were found dead as a result of suicide, accidents and natural causes in London, Hertfordshire, Sussex, Coventry, Essex and Cornwall over the past 35 years.
The appeal was the result of a review by the National Policing Improvement Agency (NPIA), which is responsible for the missing persons' bureau, and British Transport Police (BTP).
It will be followed by further reviews, starting with the south coast forces Kent, Sussex and Hampshire, where many unidentified bodies have been pulled from the sea.
Peter Neyroud, head of the NPIA, said police have not always offered a "terribly good service" when faced with relatives of missing people.
He said colleagues attempting to clear up unidentified bodies were faced with a mountain of ageing paperwork, some of which was badly compiled and in a poor condition.
Mr Neyroud, 51, said: "What we are trying to do here is create stories with endings for families who have been grieving and simply have not got an end to their story.
"Many of these cases go back almost as long as I have been around. A lot of this is to do with the fact that technology and methods of identification we have now were not available.
"It is extraordinary how many people know somebody or have somebody in their family who has gone missing. We want to work with forces across the country to find the end of some very sad stories."
The national missing person's bureau database holds the names of around 44,000 people who have been missing for more than 72 hours. Some date back 60 years.
Police have picked 20 of the "more straightforward" cases from more than 1,000 unidentified bodies who they believe they may be able to name.
They said it is "right and proper" to name the bodies, even if there is a suggestion they may have been living an anonymous life and did not want to be found.
Mr Neyroud said police have encountered some resistance from coroners when trying to reinvestigate deaths which were dealt with many years ago, particularly when trying to get DNA samples.
He said advances in DNA testing include a new technique that could yield a result in 45 minutes without the need to send a sample to a laboratory.
Detective Chief Superintendent Miles Flood, of BTP, said up to 300 people are found dead on the railway network every year, many of them itinerants.
He said: "We have obviously fully investigated these cases. There is nothing suspicious about the deaths. These are people who died from natural causes or other means.
"For me, as a professional police officer, I do not like unsolved cases and although every case was investigated and every clue followed up, we have been unable to do so.
"We are now taking another look to see if there is more we can do with advances in forensic science and through public appeals like this to identify them."
The cases date back to January 1975 when a woman was struck by a train at Victoria Tube station. The most recent was last December when a man died on tracks near Plumstead station, in south east London.
Investigators are able to draw on expertise from the National Injuries Database, DNA databases, fingerprint database, and age progression and forensic artists.
:: Anyone with any information about any of the people pictured is asked to call BTP on 0121 634 5613.