Where is the secondary responsibility?
Both the cyclists and the HGV driver have a primary responsibility to obey the Highway Code. Both have a secondary responsibility to be prepared to react to the errors of other road users which might otherwise cause an accident.
The cyclists failed to comply with their primary responsibility.
As this thread shows, the extent to which people believe the HGV driver failed to comply with his secondary responsibility is in the eye of the beholder, e.g. he should assume that that there are cyclists in his blind spot:
a. all the time
b. whenever he sees x number of cyclists pop out in front
c. in London
d. in any built up area
e. during rush hour
f. whenever there is a cyclist in his blind spot (because somehow he should know, even if it’s a blind spot).