I spent a couple of hours edging and sealing the windows and inner door in the co-working space for draughts with standard brush, d-profile and v-profile seals where necessary. These should be more effective than putting foam boards in front of the windows at stopping draughts leaking heat. The window facing the railway needs some repair and/or a second locking handle lower down, but the seals should cover it in the mean-time.
I'll take a look at the other windows too, but figured the co-working space needed it first.
Next up: The boiler-leak needing fixed, and curtains or lined roller-blinds to keep the heat in. Especially at night. We could try plastic-lining on the single-glazing, but it's pretty negligible compared to curtains. Obviously, curtains need to be cleaned (very) occasionally.
I'm likely heading to the self-build thingy for a couple of hours, but need to check with Angie.