In the grim 1950s, 40,000 people left Ireland every year to emigrate to Britain.
They built the roads and repaired the bombed out buildings of post-war Britain. They staffed the hospitals, the factories and the railways of a booming country while the economy stagnated at Ireland.
It is estimated that half of all Irish people born in the 1930s emigrated, the large majority to Britain.
They are now getting older. For many, emigration to Britain was the making of them giving them opportunities they would never have got at home.
For far too many though, Britain was a place where they never settled, where men who worked on building sites and roads were broken in mind and body by the conditions they endured.
Often a feeling of shame or inadequacy meant many never returned to Ireland and their relatives are now dead.
These "forgotten Irish" will be remembered with a plaque unveiling ceremony at the Camden Irish Centre in London on Monday afternoon.
The ceremony will be performed by the Irish ambassador to Britain Dan Mulhall.
He has pointed out that these Irish emigrants not only made a contribution to Britain, but sent back millions in remittances to an impoverished home country.
This memorial will be a sister plaque to the commemorative plaque unveiled at the East Pier in Dun Laoghaire, Dublin on May 15th, 2012.
Margaret Brown of the Friends of the Forgotten Irish said the plaques in both countries will remember those who "shook the handkerchief off the boat" as they left the pier at Dun Laoghaire to emigrate to Britain.
She said many of the forgotten Irish are lonely and suffering from poor health. “It is really a sad story. Many of them have nobody to go back to in Ireland,” she said.
London Irish Centre charity chair Dermot Murphy said the centre had been a "home-from-home" for generations of Irish immigrants to Britain in its 64 years in operation.
“ We are delighted to provide a site for this significant memorial plaque and to honour those who did so much in so many different ways to create this vibrant, special city,” he said.