Well the torch is fine. I resoldered the wire to the switch and all worked as it should.
I am as convinced as I can be that the light output is still identical with that wire added though.
The initial appearance looked the same to me when shone on a wall, but to be sure I actually photographed into the torch itself on aperture priority, so the light meter would change shutter speed if it was brighter, and they were the same.
What batteries? Is it brighter with all 4 than just 1 or 2?
Initially with just 1 lion, but when that was fine I used all four.
It is certainly brighter with 4 batteries than with just 1, and 2 seems brighter than 1 but not as bright as 4.
Did you see this link to the mosfet from earlier in the thread? It might help.
So, time to take some measurements. Measure voltage between the FET drain & source pin, and between the source pin & ground/B-.
What batteries are you using?
I found the datasheet here, none of those 3rd party datasheet sites work with my adblock-Nazi filters, they're just perpetually annoying so I try to always find the datasheet from the actual manufacturer's site.
I'm struggling a bit with the voltage measurements as I'm not really familiar with using a meter, and I'm trying to hold the driver on the batteries whilst switching it on and holding the probes in place (and I'm towards then end of a very nice bottle of Rioja). I may have to come back to that tomorrow after trying to grow another pair of hands.
However, in the meantime something very interesting happened during my cack-handed attempts, viz: When I put the measuring probes between the source pin and the middle pin by Q1, connecting them together, the luminosity pretty much doubled!
Would there be a problem created by just soldering a wire between them?
The batteries are from an OEM Dell laptop battery, with only about 20-30 cycles. I think they're about 2400mah, I can't remember the manufacturer for sure, but possibly panasonic.
Yes, the problem with doing that is that bridging those pins (drain & source) completely bypasses the FET, and the FET is the only means of turning the light on and off and getting modes.
If the light was running on high mode when you bridged those two, and the FET is what the datasheet says it is, no way should the output have increased that much. That FET is supposed to be 12 milliohms, removing that little resistance shouldn't give enough increase in output to be noticeable with anything but a light meter.
And this is the last time I'm going to ask this (isn't this the third time?): what batteries are you using?
I just tried it again to be sure, and it may or may not be double, but it certainly increases significantly and is pretty close to double. But you are right in that I cannot turn it off with those bridged.
I have answered that twice, but I think I added it both times as an edit, so you must have read the posts before I ammended them.
They are 2400mah (I think Panasonic) from a Dell laptop battery, but fairly new with only about 20-30 cycles.
This is your circuit, only slightly simplified:
I wasn't sure whether to measure voltages with the light on or off, so I did both.
Off, it was 1.5v for both source-drain and source-B-
On (high), it was 0.2-0.3v for both.
The only meter I have has a needle, rather than digital readout, but these are as accurate as I can get.
I also tried shorting across the source pin and the Q1 middle pin again, and it's definitely about twice as bright.
You need something that's fairly accurate down in the sub-100mV range. Just about any digital meter will be close enough.
OK, I'll see if I can get hold of one drekly. Thank you very much for your help.
I haven't been able to get hold of a digital meter yet, but I did find some pure copper anti-slug tape, so I've used that to try the resistor bridge again (rather than the long piece of wire I first used), and I'm happy to say the lumen increase is quite considerable! 
It is now as bright as my 3 XML Fandyfire, but flooding over a larger area and with a larger centre spot, so overall outputting more light as it should do.
It could of course still be considerably brighter, as demonstrated when I shorted the FET, but this will do for the meantime.
Thank you for your help Comfychair, and everyone else who contributed.
something cool that i found out is that the micro-controller used is likely a attiny 10 (at least one is compatible)
this means that we should be able to re-program the controller to perform more functions or more brightness
however i have not received my light yet from DX as it took a detour through the Netherlands on its way to north america.
w/ 1 Li Ion battery driving 7 LED’s the battery was the limiting factor in current flow/brightness, jumpering the resistor or not the battery could not push more current to the emitters. (Imagine a VW bug w/ a 5hp motor, just can’t push it faster, now take 4 cylinder engine and voila…more push available 
)
With a Direct Drive MOSFET, now imagine taking a V8 engine and shoehorning it in (aka very HIGH current drain batteries) NOW you got some power 
Lalalandrus: I wouldn't have a clue where to start with re-programming a driver, but you clearly do, so I shall look forward to your findings when your light finally arrives. In the meantime I shall read up on the attiny 10 and how to use it.
Warhawk AVG: You're a man after my own heart - a supercharged V8 in a go-kart is what I'm after!
I've seen a direct drive mosfet driver at Mountain Electronics which I was considering, but if I can reprogram this one as Lalalandrus believes then problem solved!
next step needs a scope.look at the drive to see pwm.
if none the gate is not being turned fully on and your mosfet is now a resistor.they dissapate lots of power as heat in this mode.
bad news! my driver is different. my driver is using still using direct drive pwm and using just the RDS on of the mosfet as a current limit.
another issue i have with my driver is that it is only 2 modes (hi and low)
new info: - turns out the third mode is long press for strobe
i cant help in re-programming your controller as the micros are different.
on another note, you can look at the pwm using these instructions: Measuring PWM
edit see what you have in beginning.its not a fet issue
rdson of modern ones are so low now that other circuit resistances are often greater.
its being used like a linear regulator in high.probably to prevent meltdown in a crap light with no thermal path to the body.