Ok, you'll know that the algorithm used by Speedtouch routers to generate the default password has been discovered, for example here:
hxxp://www.gnucitizen.org/blog/default-key-algorithm-in-thomson-and-bt-home-hub-routers

What it's not clear to me is it says the algorithm takes the router's serial number to generate ESSID and password
But the serial number is unique, right?
I'm saying this because I'm sure I found several routers with the same ESSID, that should then have the same password