https://www.consumerreports.org/head-injuries/most-cyclists-who-suffer-head-injuries-arent-wearing-helmets/
This is just one of many articles I have found on the Net which suggest you are more likely to have a head injury if you don't wear a helmet. Surely at this time of crisis an the NHS is overstretched, it is sensible to wear one to protect yourself? Besides which, logic suggests that if you fall off your bike and bash your head you are more likely to sustain a worse injury to it if you are not wearing head protection.
You have to be really careful with studies like that because the sample is biased. It's only looking at people who had a serious enough head injury to be admitted to hospital and not at people whose head injuries were so serious they didn't make it to hospital. It's also not looking at other injuries.
So let's say you look at 100 hospital admissions and you see 22 cases where the cyclist was wearing a helmet and 78 cases where the cyclist was not. You also note that 29% of all cyclists wear helmets, which is a higher proportion than the number admitted to hospital, so you conclude that wearing a cycle helmet is safer than not.
What if you then go to the mortuary and find another 50 helmet wearing riders whose necks had been instantly snapped in the accident because they had been wearing a helmet. Then you go to the other hospital ward and discover another 50 helmet wearing cyclists with broken backs because they had taken a risk that led to an accident, but they wouldn't have taken that risk in the first place if they hadn't been wearing a helmet.
It's called survivorship bias, and it works both ways. There's a famous example from WW1: after the British introduced steel helmets for the soldiers in the trenches, the field hospitals saw an
increase in head injuries. This seems counter intuitive, but the reason is simple: the extra head injuries were from soldiers who would have been dead had they not been wearing a helmet.
You need a lot more information than was presented in your study before you can start drawing conclusions about the efficacy of helmets.