Dr Alison Ross of Cancer Research UK said last night: “This is encouraging work, but it’s at a very early stage because it involves cells grown in the lab and mice. Much more research is needed.”

The team, led by Dr Qi Chen of the National Institutes of Health in Bethesda in Maryland, found a “rapid and sustained increase” in hydrogen peroxide was detected in tumour fluids within 30 minutes of starting the treatment.

An early-stage patient study showed that similar therapeutic levels of vitamin C in the blood could be achieved when it was administered intravenously in humans.

In the journal Proceedings of the National Academy of Sciences yesterday they wrote: “Concentrations decreased tumour volumes 41 to 53 per cent in diverse cancer types known for both their aggressive growth and limited treatment options.”

They said it meant the injections “may have benefits in cancers with poor prognosis and limited therapeutic options”.

Until now the role of vitamin C in fighting cancer has remained unclear, with some experts suggesting it can actually reduce the effectiveness of cancer treatments such as chemotherapy.

However, in the 1970s Professor Linus Pauling, one of the few people ever to win two Nobel prizes, was convinced about the cancer-fighting potential of vitamin C. Along with Scottish doctor Ewan Cameron he used injected vitamin C to treat 100 terminal cancer patients at the Vale of Leven District General Hospital.

The patients survived, on average, 300 days longer than expected. A follow-up four-year study by the two scientists found patients given vitamin C jabs typically survived for 343 days compared with 180 for a control group of untreated patients.

But the experiments were dismissed by peers because they did not include control groups of patients given placebos.

Later, two randomised placebo-controlled trials of vitamin C cancer treatment were carried out on 200 patients in the US. Neither showed any benefit.

However, these trials administered the vitamin by mouth and not intravenously.

According to the authors of the new study published yesterday, this makes a huge difference.