Redbeard

Very true, but a lot of authorities used it as a 'short cut'.

+1 re no gas, although of course you can have no idea of how much you will save till you get a quote. Ditto agree with @Bonner re negotiating.

Dehumidifiers will do the job if the 'box' (the house) is closed. If it's not you will be trying to dehumidify the world (and that will take a long time!). If my guess re floor level is right and that residual cavity at the bottom of Pic 1 remains open you will have a sizeable thermal bridge all around the perimeter of the house at floor level. I find it hard to imagine the intention was to leave the lower cavity open, so what was the original plan for it? @Oz07 is right, I think, that injected bonded graphite EPS beads are your only option now (and the right option, compared with Rockwool which may absorb moisture, below DPC). I have had difficulty getting EPS blowers to engage with partial jobs or 'non-standard' installations, so I hope you have better luck in your area. For such a relatively small area, but one which it is essential to 'treat' with insulation, I think whatever you have to pay is worth it. I don't have any contacts in the SE, I am afraid. I am sorry you have had a difficult time of it.

Variegated crushed stone, with a path area laid lower as a base for recycled block paviours. (Our contractor got approx 12m2 for free via Facebook when we needed to match in with some that I had laid 30 years before). That way you get a clean path and a solid (if perhaps sticky-in-the-wet - though I am sure that a better knowledge of stone than mine might also sort that one) hard-standing. If you have the space, 2 paths give clean vehicle egress for both sides of the car.

If you make your own it also has the possible advantage that it will not be left on a reel. Did anyone mention ensuring the reel is fully unwound? A hefty draw on a part-wound ext'n lead shows what a good resistor it makes... (Egg-sucking and grandmothers not intended!)

Whether the roof has flat or vaulted ceilings I would suggest cut some rigid insulation at the eaves to form a 'ventilation profile', then (if it's a flat ceiling) 200-300mm of your choice of 'quilt' on top of the joists at right angles to them, then friction-fit semi-rigid mineral wool between the joists to finish. Then VCL, then plasterboard. If it's vaulted you'll need to 'build down' from a 50mm vent path to get a B Regs compliant level of insulation. (Crudely about 150 PIR or 270 'fluff') BUT (re ventilation), The WC etc roof is a lean-to, isn't it, which presumably means there is no cross-ventilation from the eaves? So... Can you put vents in the end of the 'WC end' and the utility, to get air flowing that way. Keep the 'ventilation profiles' I refer to above as well, so you get a bit of extra supply ventilation to the void*. *Of course this only works if you have voids, and doesn't if you have vaulted ceilings. More info, please!

I don't know how likely this is, but try it: Previously you had just concrete. I assume the top pic is 'before'. Now you have mud and broken concrete. It looks as if mud has splattered up the wall and has imparted a layer which absorbs water. So is it that the bricks area completely soaked through, or that the 'mud overcoat' is wet? BTW, you said As this is a cavity wall you might not see damp internally even if the ext wall was wet. This was, after all, the original idea of cavity walls, that a failure properly to maintain the external skin would not automatically result in damp internal conditions for the tenants ('tenant' used advisedly as experimentation with cavities started in 19th C when the private rented sector accounted (if I remember my Housing lectures properly) around 90% of the housing stock. (I accept, of course, that that cavity in your pic may well have been retro-filled if it is, as I guess, c1960s).

I certainly don't think it is fussy not to want someone else's rubbish delivered to you, and I too thought that asbestos skips were, for a start, usually covered and lockable, but @Russell griffiths may be right about the grades. OTOH, however well bound it is, asbestos-bearing is asbestos-bearing, and I would not want some (insert applicable word) removing my crinkly asbestos garage sheet from an open skip to put their cr** in, leaving me with another asbestos problem to solve. A cover would go a fair way to avoiding that.

I like the way you used the cardboard cut-outs to boost the apparent numbers!😉

But that's their (or the sales person's) problem. They have delivered what you didn't order, and you want what you did order. You have every right to ask them to take these away and let you know when the correct ones are ready for delivery. If this will screw up your timetable then maybe there is a 'bird-in-the-hand argument which could be won by an additional discount. AFAICS you hold all the cards at this stage.

Is this a problem over the whole roof, or in discrete areas only? I suspect, given your description, that it is rain blowing up the laps. Although I suggested in another recent thread that sarking felt is not always 'noticeable by its absence' this may be an exposed situation where it would help. It's a bit older than mine, but not much, and I would have little hesitation re-laying at least 60% of my slates as a new roof . I have seen an example in an area of very high industrial pollution where natural slates resembled 'porridge', but if your slates look OK from the top it may well be 'cause they are.

Looks very like it. Try to get rid of the bubbles that are there and do a 'controlled experiment' with significantly smaller amounts of detergent.

Hello! Although the first bit of insulation is always the best one (the graph of insulation efficiency climbs very steeply, and for each subsequent unit flattens out further and further) 100mm on the ceilings is pretty unexciting. The Bldg Regs would require 270mm of 'fluff' (glass-fibre or Rockwool or - as per @Sparrowhawk - recycled plastic bottle insulation ) or a tiny bit less of sheep's wool, recycled cotton, flexi woodfibre etc. I would not recommend lass than 300mm. The stud walls are going to be more tricky for you because of the tight space. My minimum recommendation would normally be full fill of the stud depth, with a wind-tight breathable membrane stapled over the studs. If I could I'd put the same membrane over the ceiling insulation too, to reduce the risk of 'windwash' - cold air getting in among the layers. Are those rafters 150mm? So you could get 100mm in and still have decent ventilation between the felt and the insulation. Access would be easiest if you took the ceiling down. That could, if the pitch is steep and headroom less of an issue, allow you to add further battens and insulation under the rafters. Note the minimum suggested 270mm on the flat ceilings and possibly the 100mm+ to the stud wall may comply with current Bldg Regs. 100mm in the sloping ceilings wouldn't. Normally I advise people to make sure they do, so that on future sale they don't get would-be purchasers trying to push the price down. Others take a different viewpoint. Getting Bldg Regs approval (or not) costs. See Planning Portal for details. @Sparrowhawk has covered the rest re air-tightness and thermal by-pass.

You raise a valid issue, but I'd probably be just as worried about heat-loss via the window-board, unless you have checked and there's 75 - 100mm of PIR insulation in there. Most Oriel windows like this seem to have absolutely zilch that's insulative between the window-board and the outside world. In my experience uPVC window installers don't necessarily tend to be insulation or air-tightness specialists. As far as you can tell, what is actually supporting the window-board (and the whole oriel window structure)?

ps - site currently resembles the Somme ...and sadly probably will do until April+ Is there any scope for a rudimentary 'porch' outside the door (even if it's a free-standing 'shed') so you can have a good doormat and change wellies outside?