Left crank pedal thread slightly stripped

On the ride home from work today when ding off pops the pedal from my left crank arm. Ive got the standard sugino cranks with MKS Sylvan Lite pedals. This is the thing, just the first 1-2 threads are stripped out, the rest are perfectly fine.

So I one legged it to my local bike shop, thinking they would tell me they could re-tap the threads (heli-coil), and he just looked at me and said 'nope, needs a new arm.' Didnt try to offer to order the part for me, nothing.

Called Evans (reluctantly), and even their guy said 'i cant promise anything.' Granted, without looking at it, it was wise of him to say that over the phone, but Im a little surprised that this isnt an easier fix... I used to retap threads in car and motorcycle engines with my dad all the time...

Any suggestions as to a good bike shop? I live in New Malden (near Kingston).

I don't think it's very likely that any one would tap the threads into place. Not really worth the hassle, plus probably wouldn't be any kind of long term solution. Best to buy a new left arm or maybe even crankset. Brixton Cycles is a good shop and would give you excellent advice, they are obviously quite far away from you, but you could call and ask them their opinion.

If and this is a big if, the rest of the threads are fairly undamaged. You can as a bit of a bodge use an old pedal thread to re-cut the thread in the arm. Cut a couple of slots down the length of the old pedal thread first. This gives the metal that is going to be cut from the arm somewhere to go and creates cutting edges. Screw the pedal in a couple of threads and then remove it to clear the swarf. Progressively screw the pedal further in until it bottoms.
May be worth a try.