The Archbishop of Canterbury, who will give a blessing at the service, says he has witnessed positive things in the aftermath of the disaster.
"Community somehow seemed to emerge in a way in which many of us I think wondered if it still existed - particularly in the big urban areas.
"Secondly is the fact that people were horrified. That sense of deep horror - this is not right that this should happen in a tower block in London, are we that kind of country, and a sense that this is wrong. Both those things are signs of hope."