OK, the newspaper article is almost a full house of crash helmet mispromotion bingo right there, including the proponent being a cyclist himself, saying it's a belief and so on and so on... but let's drill down into the key bit quoted:
In 26 out of 32 secondary impact cases, helmets would have reduced the cyclists’ head injury by around 75pc, the research cited by the European Transport Safety Council (ETSC) shows."
I looked that one up and the source seems to be K. Fingleton, M. Gilchrist (2013), UCA Dublin, "A study of the protective capabilities of cycle-helmets in collisions involving motor-vehicles based on computer simulated reconstructions" which doesn't seem to be available online, does it? It doesn't even appear on
http://www.ucd.ie/eacollege/mme/staff/academicstaff/professormichaelgilchrist/staff,98866,en.html or
http://researchrepository.ucd.ie/browse?type=author&value=Gilchrist, M. D. and there's no Fingleton on their staff list or the author list. UCA is University of Creative Arts, so I suspect that's a typo as there's nothing relevant on
http://www.ucreative.ac.uk/ireland - has anyone found this paper?
Just from the title, I have my doubts about using solely computer simulations for this because a simulation is only as good as the factors it includes and reality has a bad habit of surprising us with effects we hadn't foreseen. Secondly, it sounds like it's only considering head injuries and again only cases where a collision has already happened, not population-level effects.
However, taking a step back, what does ETSC - the body whose mere
citation apparently lends credibility to that research - say are the first things to do to improve cycling safety? 30kmh urban speed limits, best practice guidelines for street design, Intelligent Speed Assist in motor vehicles, various enforcement measures, lower speed limits at junctions, priority maintenance for footways and cycleways (the opposite of most current English policy) ... cyclist crash helmets are only the very last section of
http://etsc.eu/wp-content/uploads/etsc_pin_flash_29_walking_cycling_safer.pdf - let's do the more effective measures first and if it's still not good enough, then consider crash helmets.