Enhanced Capital Allowance Scheme
There are certain technologies of which some, or all of the initial investment costs can be recuperated from the UK government. This is called Enhanced Capital Allowance or ECA.
The Air Conditioning system you thought was out of your budget range may qualify!
The questions you need to ask:
What can I claim? This link expalins what can be claimed
You will need to know the manufacturer and proposed system before entering the above link. For example: FUJITSU ABYF18LA
There are other technologies that qualify for ECA, for example some water boilers MAY qualify. You can find out if yours does by clicking on the "browse ETL" link above.
How do I claim? This link directs to the page which expalins how to claim.
Most of AACR's "heat pump" (heating and cooling) systems qualify for ECA.