Uplifting existing 60mm cavity insulation & 50mm cosy board & 100mm attic floor

On none of the above I'm afraid because your primary method of heat loss currently is likely air leakage and none of the measures listed will address this.

On paper, your house is actually reasonably well insulated and should not be costing you what it's costing for heating. However, there is likely no air tight barrier in your external walls so you are losing your heat by air leakage (convection losses) rather than by conduction (which insulation addresses generally). Getting a handle on your air tight weaknesses would likely be money well spent to drop your heating costs,

Were the insulated slabs fixed straight into block wall or were the walls plastered first?

Unplastered walls let air walk through them.

WallTite CV100 is an airtight product therefore no need to plaster walls first.

Yes, that stuff will get into every cook and cranny.

While walltite may well do a decent job on airtightness of the block work, my concern with using it would be the very real risk of cracking in the structure due to the pressure exerted by the expanding product on the cavity wall leafs.

Imo, solving one issue while introducing a real risk of creating a bigger issue is never a good idea.

There is no point in buying a thermal camera unless you are trained to interpret the images taken under the required conditions.

Good article from an industry expert.

"That's too expensive, just send me the images without analysis".

We have heard that statement 2-3 times a year for the last 21 years and I'd like to take two minutes to explain why we never just send raw thermal images to anyone, ever.

Thermal imaging is a tricky, weird service & science that requires two very important steps.

Firstly, you have to take the images in the correct conditions. If you are receiving cheap quotations from providers guaranteeing survey dates, you ought to be very suspicious. Your Spidey Sense should start to tingle. If it rains, is too windy, too warm, foggy, misty etc - you cannot survey. The laws of physics dictate this process and it cannot be side stepped or underestimated. The golden rules are 2-3 hours after sun down. Dark, dry, low wind conditions and heating on in the building.

So, assuming your images were taken in the right conditions, what's the second step? Well, analysis is the answer to that question. Have you set the level and span properly, the emissivity, humidity, distance to object? Do you understand the thermodynamics at play? The construction details that cause cold bridging? Again, Spidey senses should tingle if your chosen provider doesn't understand how buildings are built or is willing to send you raw images and an invoice..

21 years ago thermal cameras were £40K. Today, they are around £6-7K for a similar spec camera. That fall in price has lead to more and more start ups entering the market, which is fantastic - it validates the technology and helps people raise finance to grow their companies - but it also means people are entering the market without the experience needed to do it properly. £40K means you think about it quite a bit before investing it. (The drone market is very similar).

That aside, please don't ask anyone for images without analysis. It is far too easy to misinterpret an image and make an expensive mistake. eg take an image on a hot day, your building will look like it's badly insulated. If you can't see when the image was taken you could conceivably spend thousands of pounds scaffolding a building to extract perfectly good insulation and put a tenant into fuel poverty.

If a surveyor is willing to send you un-analysed images - you should run a mile.

@boardtc any update on Walltite, did you get quote / proceed?