Officially opened on 11th September 2003, the garden features a central plaque dedicated to British victims of the attacks on the World Trade Centre in New York and the Pentagon in Virginia. The garden features an oak pergola and a pavilion, with the words "Grief is the price we pay for love", which were used by the Queen at a New York remembrance service a week after the attacks.
The garden also features white Bianca Roses which are, we are told, a significant flower for British families of those who died on September 11th. Though a new memorial has recently been unveiled in Battersea Park, this is still a very important location for the families of those who died.
For more, see http://london.usembassy.gov/grsvnrsq/911mem.html