The Great British insulation Scheme

Need to have low levels of insulation ( or none )

Council tax Band A-D ( England ) A-E Scotland and Wales
EPC D-G

Tenants can apply !

there are already lots of sites pushing this ( and no doubt some will be scams ) but 

octopus.energy/great-british-insulation-scheme/#:~:text=The%20Great%20British%20Insulation%20Scheme%20is%20government%20funded%20and%20designed,reduced%20costs%20for%20home%20insulation.  For Octopus Customers

www.gov.uk/apply-great-british-insulation-scheme the official Government site

If you get benefits should be free, others you may pay 10% 

it only covers 1 upgrade so External Wall or Loft ( not both ) other upgrades available.
Given I had a quote of £14K for Wall insulation ( that was for the back wall only) if I could get it for under £2,000 I'd go for it.
I'm 64 so even if I got £1,000 a year ROI then I'd be 78 before breaking even, but given a gas bill of around £800 a year for 8,000 kWh it would need to send my heating bill negative.
At circa £2,000 then if I could halve my gas bill then 5 years, and a more likely 10 years.