Re: The law is wrong
The act of arming yourself equates to premeditation - they aren't carrying a knife because they're going hiking, in Peckham / wherever. The intention to kill is obvious, and its time the law was tightened to remove this wriggle room around intent. If you stab someone, unless you can prove otherwise, the safest way to proceed is to assume you intended to kill them.
Homicide != Murder
Heck, even intending to kill someone does not automatically imply murder.
Murder (in the UK) is "the unlawful killing of a human being in the Queen's peace, with malice aforethought".
Note - "unlawful", and "malice aforethought". The entire concept of murder (as distinguished from homicide) is predicated on intent.
If someone is kicking down my front door and I go to the kitchen and get a big knife (having called the Police), and they come through the door and get that knife through their chest because the rozzers haven't showed up in time, then it's homicide (one person killing another). It's even intentional. But it's not murder, and no sane CPS solicitor is going to try and press a prosecution, because the door is hanging off it's hinges and there's a pretty clear mitigating circumstance.
You can't just remove "intent" from consideration - the offence is defined by intent!