I'm hanging on to see if solar panels get subsidised. Plus I suppose it makes sense to get insulated first.
The HES post-survey technical reports are quite good.
Currently HES isn't funding solar PV panels other than providing the interest-free loans. For solar thermal they are doing substantial cash-back on top of the loan, but only once the work is confirmed complete.
HES is very picky about the homeowner not commissioning any work until they have applied for the loan and had it approved. My CWI installer, a well known company that has done many housing association projects, quoted for the work and that quotation was only valid for 30 days, and they needed paid upfront a minimum of seven days before the work started. Remember that a HES loan application requires an EPC that is no more than three years old and (obviously) it must list as a recommendation the work you plan to have done. My EPC was five years old, which meant I would have to commission a new one solely to get my CWI funded. Or rather, part-funded: an EPC costs £75-100, and you must also update your EPC once the works are complete. Of course, you can include those costs in your loan, except that the CWI loan is to a maximum of £1000. For my really not very big house the work was £1300, plus a notional 2 x EPCs. 40% cash-back sounds like a lot, but half of that would have been absorbed by the EPCs, so I was set to save myself perhaps only £200 all told.
30 days simply wasn't long enough for me to get a new EPC and for HES to turn around a loan application. In the end I told them I had been cold in my house for four years and I was so fed up with the whole thing that I would just pay the costs myself and get a new EPC later when I do solar and/or a battery and ASHP. My local authority is utterly useless (in multiple ways) and had no area-wide schemes I could take advantage of, and of course I don't qualify for any other sort of assistance. My oil boiler is over 25 years old and I still don't qualify.
The only thing in my favour is that I have the use of an eyewateringly expensive FLIR camera, and am qualified to carry out my own post-installation thermographic survey.