Hello all.

Thanks for all the replies.

I will be fitting new sash cords.
I will replace the broken parting beads on both sides (not the whole beads,
as it will be too much work; it's a _large_ window, and the kitchen sink
assembly reduces access by two thirds).
I've ordered 4 half pound makeweights, and 2 Grabba (does away with nailing
the sash cords) from Mighton Products.
The bits should arrive on Monday.
I'll start by adding one half pound makeweight to each side, and hope that
this will be enough.
The "Grabba" is meant to make fitting and adjustment of the sash cord
easier. I have no idea how it works as there was no explanation or
illustration on the website.
If you want to use Mightons, be warned: the only delivery method (overnight,
next day) costs £10.30.

Sylvain.