The UK is not more violent than America. Most years we have less than 1000 murders total across every single type of murder, the US has 10x that from firearms alone with only a 6x larger population. You hit on the reason why our violent crime seems to be so high, almost every crime that could be violent is counted as violent (for example if someone broke into my apartment while I was out) and in most other countries that isn't the case. What crimes does the UK have (that are violent) that are higher in number than America? Every single crime type that I've been able to find comparative statistics for shows the US to be higher. The UK certainly isn't a crime free utopia where nobody locks their doors but it is not the violent place you paint it as, especially when compared to the US.
The different between the two estimates - derived from the questioning of
around 600 under-25s about whether they had been "knifed or stabbed",
and then extrapolated to the wider population, with all the statistical
vagaries that entails - reflects the lack of precise information about the
scale of knife crime in England and Wales.
Higher in actual number is almost always going to be relative to the population, isn't it? Per capita is more accurate while it still is lacking for comparison purposes.
I agree that murder, as one type of violent crime, is more prominent here in the US than in the UK on a per capita basis.
Crime stats are most definitely open to a lot of interpretation between countries, actual reported statistics vs unreported, varying definitions, and more.
Also for some hilarious reading, why not read this article from THE SAME publication that you linked to that says the UK has a massive knife crime problem: http://www.telegraph.co.uk/news/uknews/1546085/The-vagaries-...