Knocked down the rest of the wall and removed the door frame, and tried to tidy up the edges a bit but gave up soon enough realising it would be easier to tidy up the edges once the new wall is in.
I've used 16mm smooth bore plastic ducting, it's held in place with ordinary gypsum plaster to make sure it will stay INSIDE the wall and not pop out.
Also cut out the hole for the central heating (left) with 53cm distance between the two to fit onto a 60x140cm radiator.
All ready and insulated to go into the wall.
Annndddd the start of a wall, I did the two corner blocks yesterday and got them levelled out on a mortar bed, and did the rest today, also on a bed of mortar, took a fair old while to get them pretty level and in line with a string, but should be easy going from now on! (With a bit of help of the planer to get started.)
Should really get a bottle of champagne out and celebrate the first straight wall in the house, as well as the first perfect (90 deg) angle wall in the house!