Reductions in the department of energy and climate change’s (DECC) budget could lower staffing levels by 90%, according to analysis by the Green Alliance think tank.

The department’s budget is facing cuts of as much as 50% but with large portions of the remaining resources ring-fenced (mainly for nuclear decommissioning) the impact on other spending is heightened.

“Less than a fifth of DECC’s budget is spent on its core mission of reducing energy costs and accelerating low carbon energy investment,” said Matthew Spencer, director of Green Alliance. Spending reductions will focus on these areas because the department is lumbered with huge historic liabilities from the nuclear and coal industries. The government’s ability to get a good deal for current consumers and future citizens will decline rapidly unless DECC gets a much better settlement than predicted in next week’s Budget.”

It is thought that DECC’s budget could be cut by 50% by 2017-18 with the knock-on effects for staffing budgets being felt in 2018-19.

A group of senior energy academics have written to Oliver Letwin, the minister for government policy urging caution.

One of the signatories, Paul Ekins OBE, professor of resources and environmental policy at University College London, said: “The prime minister went into the general election with an admirable commitment to deliver a low carbon energy system for the UK. DECC civil servants are already very stretched in delivering this historic imperative. We are concerned that the next round of budget reductions could inadvertently undermine the government’s ability to complete its important energy market reforms and deliver climate policy.”

The letter comes ahead of the Chancellor’s emergency budget on 8 July.

“Costs to consumers from energy policy are likely to be higher, and energy supply less secure, if government does not protect its in-house expertise to negotiate contracts with the energy industry, to complete energy market reform, and to develop new energy saving programmes for the most vulnerable customers,” the academics wrote in their letter to Letwin. “It is also vital that government protects its impressive track record in climate diplomacy and developing innovative carbon reduction policy, given that we have so much work still to do to reduce emissions and slow the rate of climate change.”