Already answered this elsewhere, but the scheme comes to and end on the 31st of March 2022, so if your'e considering a renewables installation then keep this deadline in mind.

A scheme called the Clean Heat Grant is under discussion ATM, and if it has a green light then that will give people an opportunity to claim a one-off payment of £4,000.00, and is proposed to replace the under-achieving predecessor,  the RHI scheme, which has failed to meet its targets for 2022 ( of 15% converted to renewables ) and is estimated to achieve about 8-10%. The CHG is, I believe, to dispense the remaining funds allocated in the RHI coffers.

The Green Deal may also contribute towards the capital expenditure of a conversion to renewables, fortifying the RHI payments, so y'all need to do the homework, ask the questions, and get clued up before the RHI and the £2bn is gone.

The above is not definitive, so do your own diligence please and ask questions accordingly, as some will, and some won't be eligible for X/Y/Z.  

Flat rate payment? That would be a significant improvement for anything with halfway decent insulation.