Ok, another aborted flight due to this problem.  This is something that has been known to CS since April 2019.  I have no other issues with this aircraft but this problem renders the plane unflyable. 

I watched a youtube video of someone else with a similar problem ( the originator of the first post, stuck autothrottle). But unlike his problem, mine does this with the AT armed. It just starts to speed up then I get the overspeed warning and by that time my throttles have locked and trying Marks fix doesn't work for me.

Looks like I now have to spend another 108 UK pounds to buy that other 777, but at least in doesn't seem to suffer from the CS problem.

Thanks,

Rory