The Conservatives have accused the chancellor of trying to “ring fence a black hole” over his pledge to protect spending on frontline services in the pre-Budget report.

Chancellor Alistair Darling said that spending on the NHS would continue to increase above inflation after 2011.

But in reference to the spending guarantee, shadow chancellor George Osborne said: “He is trying to ring fence a black hole.”

He also said that while Mr Darling had talked about preserving frontline services, including hospitals and schools, he had “stayed silent on where the axe will actually fall”.

“This has got nothing to do with protecting frontline services but everything to do with protecting themselves,” he said.

Speaking on Conservative policy to aid the economic recovery, Mr Osborne said: “We will expect everyone to share the burden but protect the lowest paid.”

However, Mr Darling replied that Mr Osborne had failed to say where the Tories themselves stood on protecting frontline NHS services and schools.

“He says absolutely nothing about that,” he said. “They can’t say what actions they will take either in protecting services or reducing debt,” he added.