I ran!!!! It was only 3Km, and at a very easy pace, but I ran! I paid a great deal of attention to not stressing the tendon, and although I can feel a little tightness/tenderness, it didn't hurt, and it seems to have got through the run without any ill effects.
I plan to rest it now, perhaps go to the gym tomorrow, and if it looks ok, I'll do Parkrun on Saturday. The club usually organises a longish run on Sunday mornings, so I might also tag along with that.
QE Olympic Park 10K in 10 days! I suspect that will be a matter of enjoying the occasion rather than going for a PB.