Up to 70 per cent of cases of malignant melanoma could be sparked by a genetic mutation caused by ageing and over-exposure to the sun.

Scientists at The Institute of Cancer Research had previously linked the rogue version of the so-called BRAF gene to the disease but did not know if it actually caused the cancer.

Now, the same group of researchers has shown that acquiring the BRAF mutation can be the first event in the cascade of genetic changes that eventually leads to melanoma, the most deadly form of skin cancer.

While the mutation could occur naturally, the odds of it appearing are likely to be exacerbated by intensive exposure to the sun.

Lead author Professor Richard Marais from the institute said: 'We know that excessive sun exposure is the main cause of skin cancer, but not much is known about the genetics behind it.

'Our study shows that the genetic damage of BRAF is the first step in skin cancer development.

'Understanding this process will help us develop more effective treatments for the disease.'

There are around 9,500 new cases of malignant melanoma and more than 2,300 deaths from the disease each year in the UK.

Over-exposure to sunlight causes at least two thirds of all malignant melanomas and up to 90 per cent of other skin cancers. This excessive exposure damages DNA and causes genetic mutations.