Here's some brief stats for 2007 :
Pedestrians : 30,191 casualties with 646 killed - 2.14 %
Cyclists : 16,195 casualties with 136 killed - 0.84%
Motorcyclists : 23,459 with 588 killed - 2.51 %
Cars : 161,433 casualties with 1,432 killed - 0.89 %
Buses / Coaches : 7,079 casualties with 12 killed - 0.17 %
Goods Vehicles : 7,816 casualties with 110 killed - 1.41 %
So the highest number of vulnerable road users killed was pedestrians with over 2% of casualties being deaths compared with 0.84% of cycling casualties being killed.
Without having the exact numbers of cyclists/motorists/motorcyclists on the road its hard to get an approximate estimation of the risk.
However there are stats to calculate number of deaths per 100 million kilometres travelled :
Cyclists : 3.5 deaths
Motorcyclists : 13 deaths
Cars : 0.9 deaths
Buses / Coaches : 2.2 deaths
Goods Vehicles : 1.6 deaths
Based on those stats, in theory you would have to cycle 28,571,428.5 kms or 17,857,142.9 miles to hit the statistical number to possibly die in a fatal accident.
As an aside there is also a breakdown of injuries per area for cyclists, of all pedal cycling injuries - 39% head/face, 2% neck, upper back 5%, arms/shoulders 43%, lower back 8%, legs/hips 24%. I tend to wear a helmet!! But looking at that breakdown I may start wearing body armour!
Morbid reading in a morning but if you wanted the exact facts or statistics...!!