In a situation that shouldn’t need any exaggeration, the Daily Kos have taken an incomplete Wikipedia list of people killed by UK police and acted as if it was a comprehensive list, comparing it to a list of people killed by police in the USA in March. The UK list is most certainly not comprehensive, and acting like it is is manipulative and very misleading.
So while 111 people killed by US police in March is incredible in itself, the claim that it is more than the UK police have killed in 115 years is absurd. This summary of deaths in police custody in the UK has the number at 1508 since 1990. That is an average of 60 per month – which is now comparable to the 111 in March, and potentially means that the UK kill significantly more people, per capita, than the US do!
However, that would be to make the same mistake as the original Daily Kos writer did, because these numbers are still incomparable. The data from the Inquest study comes from a much broader definition of death in police custody:
INQUEST defines police custody deaths as deaths that take place while the individual is in contact with police, whether or not they have been arrested, or that happen shortly after that contact. The death may not necessarily have occurred inside a police station. We do not include self-inflicted deaths following contact with police or deaths as a result of domestic violence where the police have been involved.
Meanwhile, the 111 deaths in March is taken from a website which only tracks deaths mentioned in the media. It is unlikely that this very-indirect method of counting deaths is anywhere near as rigorous as the study completed by the UK Inquest group which uses Casework files. For example, the 111 deaths cited in the Daily Kos story has now grown to 115. Obviously not all stories are immediately discovered and added – and who knows how many deaths receive no news coverage at all?
Basically, you just can’t compare these numbers. So don’t pretend you can.