I think Lush and British Red are talking about different things, that overlap.
I tend to agree with British Red, I carry a group of items that do the job of a PSK, but I do try to carry a PSK as well.
This thread does raise some interesting points.
It really worries me when people start saying I will not need one because I can be rescued, or because I have all this kit in my ruc. As you skid down the bank, twisting your ankle, and watching your ruc float away on the river. Murphy's Law says that your phone will not work, then what? For a start, in a city you can expect an ambulance in 8 minutes, but what is the response time of Mountain rescue, say 2 hours, depending on were you are, and if you can tell them were you are.
I do not know the figures, but people die in the UK outdoors, every year, so how far is need PSK. More importantly, do you want risk being one of them.
Lets say 20 miles, from help. What happens to that distance if you twisted your ankle. What happens to that distance if the way you came is blocked.
Think England too small, what about the floods? You are out walking, and get cut off, what do we think would be the response time then. You only went for a walk, that trapping wire is suddenly looking useful.
Here is the thing for me, do I carry a FA because I want to have accidents, or because I want to survive them.
A thing on mobile phones, do not expect to be able to make calls in the middle of nowhere. The 95% coverage is people, not area, so sometimes on certain networks you just will not have signal. There are still big parts of the UK with no motorways, often the very places we want to go to. More importantly, it goes to the GPS and a map question, why carry a map with a GPS, because it does not need batteries and it will work in all weathers, conditions, and is hard to very break. My point being do you carry a spare battery for your phone.
I must say it does tend to not be were it should be, and ends up in the bottom of my ruc. The point of a PSK is to give you the bare minmium to keep yourself alive, until you can get back to civililastion. Which is one of the reasons I am going for the responce pak idea so it is always in the bottom of there instead.
I have had a few of those wire saws, if you shop around and look after it they are useful, but some are complete rubbish. They do tend to be the thing, that when you want to use then they break, so they make checking your PSK a least once a month worthwhile.
I carry matches for convience, but not in my PSK.