Why was Bethnal Green Tube disaster memorial delayed?
3 March 2013 Last updated at 16:41 GMT
The worst civilian disaster of World War II is being marked on the 70th anniversary of the Bethnal Green Tube disaster.
A total of 173 people, including 62 children, died in a crush on 3 March 1943, when people rushed to enter the station after hearing air-raid sirens.
The alarm turned out to be a test.
Dr Toby Butler from the University of East London, who is leading a project to record the memories of survivors and rescuers and the relatives of those who died, said it was ''a puzzle'' why a memorial had not been realised earlier.
''This was wartime and there were concerns about morale,'' he said.
The trauma of the event was also a factor, he added.