Deaths per cyclist per kilometre of road is a crazy unit of measurement. I mean, sometimes you have to report the statistic you've got rather than the statistic you'd like, but I don't see what possible practical significance this has.

The statistic we'd like to know is deaths per kilometre cycled. The average person in the UK cycles about 60 km a year (source: Department for Transport) and the population of London is about 8.5 million (source: Wikipedia), so the 19 deaths in 2006 correspond to about 3.5 deaths per 100 million kilometres cycled.

This is slightly higher than the UK average of 3.1 deaths per 100 million kilometres cycled, and on the high side for Western Europe (compare Netherlands: 1.0; Germany: 1.8; France: 3.1; Italy: 3.4).