Well, I tried blow torch but it just melted the entire solder and the spout fell off completely, also tarnished the stainless steel finish. So now that the spout came out completely, I used this opportunity to clean all the surfaces which needed soldring and hence managed to solder it back on using a 60Watt Weller soldering iron, which is temperature controlled and so I raised its temperature to 420c and it did the job, except at just one little spot where the solder just would not wet, due to rosin based flux, so may be tomorrow I will try more stronger flux as used in plumbing, I could not find my tub of flux hence I was forced to use the rosin based flux.
and yes that 60watt soldering iron did a perfect job, the heat conduction in stainless steel (thin gauge) is not a problem for this beast of an iron, so I have no idea why you got so alrmed, had it been thicker material or better conductor of heat it would have caused problems, but it didn't fortunately, and I googled in the end someone suggested not using flame heating as it oxidises cleaned surfaces and overheats the flux, and suggested using abeefy soldering iron, and preheat the steel using a blow torch from the inside, but I found i didn't need to do this with my 60watt Iron. ( as for beggers belief, unless you have tried first only then say so) but prior to this leak, I could have sworn and never thought this spout was soldered on! I thought it was some how spot welded, but it is clearly soldered on.
I took it for guaranteed that stainless steel could not be soldered!
As for guarantee, this kettle has already been exchanged once when the previous one had its lid fall off, and when I asked Russel Hobbs parts department, they did not do lids, so offered me this kettle at substantially reduced price, I took this offer and since the first kettle was about 7 months old when it was exchanged, and this one is already now 4 to 5 months so I guess there won't be any more guarantee left on this, and it would mean I will have to take it back to the Argos and lose my time and money, already bthe leak is substantially reduced to a drop or two every minute as opposed to a small stream every time I poured hot water into cups.