Flat uPVC fascia board in black?

Yes:

Alan.

Thanks Alan but I see those are 9mm and sold as soffit boards. I've been told (by suppliers and local merchants) that soffit boards like that would be too thin without a backing board (even if I doubled them up); and that I really need the 16mm or 18mm boards designed to replace the fascia. Was that duff advice pl?

I wouldn't fix guttering to 9mm soffit boards. They do black 16mm facia if you click on the left hand menu.

Yes, thanks. But it all appears to have the "lip" (typically 16mm or more) which is designed to support a soffit board and which would make the fascia stand too far off the wall for my roof. I'm really after a flat board like for example the one at the top of

Given the number of Victorian terraces with fascias fitted like this to the back I feel I must be missing something. But at least it's an excuse to be a here rather than up the ladders - albeit it's a balmy -1 C in this heat island :)

You could cut the lip off.

The lip is easily cut off with a hand saw by laying the saw flat on the back of the board and using that as a guide. The cut edge is hidden against the wall and you don't reduce the width of the board.

MBQ

Use white.

There's a reason why black isn't popular and that is because it expands and warps too much in summer.

If needs be, replace the gutteriing in white too, although black gutter on white fascias looks good to me, and millions of others, judging by the amount of it I see every day.