Ducting is like: http://www.ebay.co.uk/itm/4-Compartment-Flat-ducting-230mm-x-30mm-/262404773959
Out of stock there and I can't seem to find a supplier anywhere else. There's not much space between plasterboard and concrete and it runs right across a room, so options are a little limited.
Flat was built about 20 years ago, so it's not that old...
Anyone seen this type before or know a supplier?