The UK does not count homicides until someone has been arrested, tried, convicted, and the appeals process has been completed. If the process does not go to completion – there is no murder counted. And of course, if the process does complete the “murder” is counted in the year the process completes.
Working backward from the deliberately skimpy data on the UK’s conviction and successful appeal rates that I have, combined with the “official homicide numbers,” the UK homicide rate is somewhere upwards of 6 per 100,000 population per year.
Bottom line? The actual UK homicide rate is probably more than one third higher than the US homicide rate.