Was UK source of massive denial of service attack on US?

Story says the source of the attacks was Uk. That is a fair comment. the UK should have sufficient control to prevent ISPs and datacentres in its geography launching this sort of attack, regardless of who commissioned it in the first place. It is perfectly feasible that the attack was bought 'off the shelf' - but it is important ot find the site from which the attack was launched, as well as the ultimate controllers. Remember McCollo?

The title is misleading; the source might be a UK based server but actually that would suggest to me it is entirely unlikely that the attackers originate from the UK

It's not hard to buy servers in the UK from abroad - and doing so is sensible (and these crackers seem sensible) because it is one extra layer of security :)

"The results contradict assertions made by some in the US and South Korean governments that North Korea was behind the attack. Security analysts had been skeptical of the claims, which were reportedly made in off-the-record briefings and for which proof was never delivered."

Exactly. As I said before claiming NK did it is utter nonsense. They don't have the resources for it.