The Transport department is making £700m in savings from roads projects, with the A38 Derby Junctions and A46 Newark Bypass scheme being considered for cancellation.
The Department for Energy Security and Net Zero is finding an additional £2bn from its budget, mainly through “efficiency” savings.
But Downing Street could not provide a full list of other projects that could be axed, saying further details would be set out in the autumn.
Transport is likely to be in the firing line because it has a large capital spending budget and the PM’s official spokesman could not rule out cuts to rail as well as road projects.
He said frontline NHS services would be protected but asked if new hospital projects could be affected, he would only commit to sites in the “first wave” of the New Hospital Programme and work on seven sites found to have been built with dangerous reinforced autoclaved aerated concrete (RAAC).
Plans to cancel the road projects have already sparked a backlash from local leaders and MPs, with Labour’s East Midlands mayor Claire Ward calling them “completely unacceptable”.
Reform UK MP Robert Jenrick, who represents Newark, also weighed in, saying: “I have written to the transport secretary and demanded an urgent explanation for local residents.
“It is shameful that such a big decision has been snuck out by the government without any debate.”
Lincoln MP Hamish Falconer, a Foreign Office minister, has said he was “disappointed by the uncertainty” around the A46 scheme, while Mid Derbyshire Labour MP Jonathan Davies said cutting transport spending risked putting a “brake on economic growth”.
Asked what Sir Keir’s message was to Ward and MPs angry about cuts to the road programme, the PM’s spokesman said: “We are prioritising Britain’s security in a more dangerous world.”