The brainchild of a Nottingham University cancer specialist, it could provide vital early warning of lung and breast cancers – diseases that between them claim almost 50,000 lives annually.

Picking up the cancer at the earliest stages when it is easiest to treat could save thousands of lives and spare many others the pain and distress of prolonged illness.

Despite advances in drugs and technology, cancer still affects almost 300,000 Britons each year – and kills more than half.

The UK’s record in treating cancer is particularly poor, with female patients more likely to die than in most western European countries.

In many cases, the sufferers is symptom-free until relatively late on in the course of the cancer, meaning the disease is not detected until it is too late.

Diagnostic techniques such as scans and biopsies focus on tumours that have already formed but the new test can detect that something is wrong well before the cancer does any damage.

The Oncimmume test picks up telltale signs of a germinating cancer in the blood. The signals – generated by the immune system – can be detected up to five years before a cancer is spotted, from just two teaspoons of blood.

Professor John Robertson, the breast cancer specialist who spent 15 years developing the test, said: ‘We are starting to understand carcinogenesis in a way that we have never seen before – seeing which proteins are going wrong and how your immune system responds.

‘It’s as if your body is shouting “I’ve got cancer” way before a tumour can be detected.

Presentations on the technology are due to be made at the American Society of Clinical Oncology’s annual conference in Chicago next week.

The kit is twice as good at detecting lung cancer as CT scans and is as accurate at picking up breast cancer in younger women as mammograms.

The lung cancer test is already in use in the US. It is due to go on sale in Britain in the first half of 2011 and will be targeted at long-term smokers and others thought to be at high risk of the disease.

She believes the vaccine could be adapted to fight other tumours.

News of the development comes as another group of scientists unveiled evidence that over-production of breast stem cells could be the cause of most breast cancers, potentially leading to new treatments.

The findings, published in the journal Nature, show that hormones released during the menstrual cycle could cause a surge in the number of breast stem cells.

Dr Rama Khokha, of the Ontario Cancer Institute in Toronto, said: ‘We are convinced that breast stem cells are seeds for breast cancer and that they are the primary cause of breast cancer.

‘Even if the cancer has been triggered by other factors such as genetic inheritance or age or density of the breast, we think the cancer is started by the stem cells.’