During the second world war, many Londoners did not have gardens and due to the fact that authorities closed nearby Underground stations eg. Oval, were forced to seek shelter in communal trench shelters. The trench shelters were considered unsafe on account of their structure, as nearby reverberations could cause the sides to cave in. That's exactly what happened on October 16th 1940 when a 15lb bomb fell directly on the shelter in Kennington Park. The estimated death toll was 104, but only 48 bodies were recovered. The rest are still lying beneath the park.
The massive death toll at Kennington Park is widely considered to have been hushed up by the authorities, on account of damaging Londoner's morale and alerting the Axis' pilots to the presence of additional civilians. It wasn't until 2003 that the specific event in Kennington Park (which saw the highest number of casualties in Lambeth during WW2) received its own memorial.
For more info (and the sources from where I drew the above), take a look at a Friends of Kennington Park guide named "Kennington's Forgotton Tragedy" authored by Rob Pateman, this recent BBC article, also by Rob Pateman and a further article on the WW2 Today website.
Gordon Johnston, Chair of the Friends of Kennington Park, introduced the order of ceremony and the Mayor. The words on the memorial are by Maya Angelou:
Cllr Catherine Bowman, representing Southwark Council helped to plant a memorial rose bush:
Pauline Harrison, a relative of two victims of the air-raid shelter, and representing the relatives of those who died in the blast, also planted a rosebush:
A representative from the Friends of Kennington Park planted a rose bush:
And finally, local children from Archbishop Sumner Primary school planted a rose bush:
With that, the evocative bugles sounded, and coincidentally a bi-plane flew over Kennington Park, and we remembered those that will not grow old and whom the years will not condemn: