Campaigners say the slowdown in the upgrade of homes across Great Britain under the flagship government scheme is 'hugely worrying'.
Under the Energy Company Obligation (ECO) scheme, energy suppliers have to provide eligible households with free fuel-saving measures, such as loft or wall insulation or replacement boilers.
Ofgem says it is a key part of the Government’s commitment to reduce greenhouse gas emissions by 80 per cent by 2050.
In Nottinghamshire, there were 2,107 energy efficiency upgrades installed in the 12 months to December, according to the latest figures from the Department of Business, Energy and Industrial Strategy.
This was a fall of 49 per cent compared to the same period in 2016.
The latest national figures show there were 12,500 improvements made to homes across Great Britain in February.
This is a fall of 33 per cent compared to the same period in 2013, and 84% lower than a peak of 76,500 in 2014.
In total, 30,675 measures have been installed in 24,283 homes in Nottinghamshire since the scheme was launched in 2013.
This means 70 in every 1,000 households have benefitted from at least one ECO measure – lower than the national average of 73.
Green Party MP Caroline Lucas said the fall in support for fuel-poor households was "morally indefensible".
She added: "These numbers provide yet more evidence that the Conservatives have all but given up on the climate crisis.
"Not only that, they’re condemning two million people across the UK to continue living in fuel poverty."
Peter Smith, director of policy and research at anti-fuel poverty charity National Energy Action, said: "ECO in isolation is not sufficient to meet statutory fuel poverty commitments, and it’s hugely worrying the rate of home energy efficiency improvements continues to dramatically slow, particularly in England."
The charity wants to see new central investment to tackle fuel poverty introduced in the upcoming government spending review, he added, which would also improve local air quality and reduce health and social care costs.