New cancer statistics show that four in 10 Britons will get the disease in their lifetime, as incidence of cancers rise, says charity

It was one of the starkest statistics about the nation's health – that one in three of us would get cancer. Sadly, the figures have just got worse. Cancer experts now believe 42% of Britons will get the disease.

Macmillan Cancer Support has revised the figure after its researchers analysed official data covering diagnosis of cancer, death from the disease and overall mortality. Of the 585,000 people who died in the UK in 2008, 246,000 of them – 42% – had been diagnosed with cancer at some point.

The one in three figure has been used by cancer experts, campaigners and ministers for a decade. It is based on the fact that research into every death in the UK in 1999 showed that 220,000 people – some 35% of the 630,000 total deaths – had previously been found to have the disease.

The new figures tally with recent research that the incidence of cancer is rising, mainly due to the UK's ageing population.

"It is alarming that the number of people who will get cancer is now well past one in three, and that there are so many more people with cancer today than even 10 years ago," said Ciaran Devane, Macmillan's chief executive.

"These figures highlight the increasing impact that cancer can have on so many of our lives," said Dr Clare Gerada, chair of the Royal College of GPs.

About 310,000 people were diagnosed with cancer in 2008, and 157,000 died from it. The number of people developing the disease is estimated to be rising by 3.2% a year because of ageing and other factors such as increasing obesity and some cancers emerging later in people's lives, after they have spent many years smoking.

The figure for the number of Britons alive who have or have had cancer at some point has recently been increased from 1.5 million to 2 million. But Devane warned that this, too, is set to rise sharply. "There are currently 2 million people living with cancer in the UK and that number is doubling to 4 million over the next 20 years. Yet no one thinks the country can afford to double its spending on cancer," Devane said.

More positively, improvements in diagnosis and treatment mean survival from some cancers is increasing, too. "Survival rates have doubled over the last 40 years, and this is one of the success stories of modern medicine," said Henry Scowcroft, Cancer Research UK's science information manager.

Gerada said: "Thanks to clinical advances and brilliant research, we are now more likely to know people living with cancer, rather than dying from it. If diagnosed early enough, cancers such as breast, skin and colon cancers are treatable, and many patients will go on to live long and healthy lives. Early diagnosis is vital, and this depends largely on patients presenting to their GPs as early as possible, and GPs having greater access to diagnostics."

GPs are working hard to improve their early diagnosis of cancer, added Gerada. Failings on that have been blamed for Britain's poor survival rates compared with other European and western countries.