According to the information provided, the UK’s ECO4 scheme supports the lowest income households, targeting those receiving means tested benefits.

Up to 50% of the obligation target under the ECO4 Flex reform can be met, designed to target low-income households that do not receive benefits.

The scheme is voluntary for local, Scottish and Welsh governments and obligated providers. The qualifying group for ECO4 Flex must be at least 3.5 million households.

Therefore, it can be concluded that although the ECO4 program includes provisions to support means-tested subsidy households, it is also geared towards low-income households who can not receive subsidies. The scheme aims to provide heating and energy-saving measures to eligible homes in England, Scotland and Wales.