Re: English drummer killed in attack.
It's not the middle of London. Woolwich is a suburb and a particularly deprived and Police-poor one at that. Absolutely the are arguments that British Police should be more readily available and perhaps armed but there are also equally valid arguments (that I support) against arming the ordinary Police officers.
The armed Police are a particular unit that are generally quick-response. The truth is that almost anywhere outside of the centres of cities that the Police response time is relatively slow - armed or otherwise. I have no idea what US Policing is like (other than they are armed as a matter of course) and it may be that your standard response times are quicker but in the UK there has been a history of a lack of Police in needed areas. Whether or not they were armed with firearms is irrelevant - most Police officers now have access to non-lethal weaponry like tasers which in this case would have an effective stand-off range to take on an attacker armed with a machete. It just so happens in this case, the armed Police were called. Other Police officers at that time (if present) would have sealed off the area and not confronted the attackers as a matter of procedure. Once the armed Police are there, all other forces take the back seat.
The full details of what exactly happened after the incident and before the Police arrived are not entirely clear. I know there are some frankly shocking images of a member of the public talking to an attacker - which is brave to say the least - but in the UK the Police are very rarely 'just around the corner', especially in deprived areas like Woolwich.
I know Woolwich quite well, incidentally. It's not a particularly bad area of London (Southwark and Tower Hamlets are worse) but there is definitely an issue with a lack of Police presence.
Reading a further news story, the response time was actually 13 minutes, not twenty. For armed Police in the UK - that is quick. For any Police in the UK, that is quick...