Rates of the deadliest form of skin cancer have reached an all time high in the UK, worrying new analysis has revealed. 

Nearly 21,000 Britons are diagnosed with melanoma each year, according to data from Cancer Research UK. 

Cases of the disease, which kills around 2,500 each year, are set to continue to soar -increasing to 26,500 new cases a year by 2040 - says the charity. 

Primarily caused by sun exposure, more than 80 per cent of melanoma cases are preventable.

Women are more likely than men to be diagnosed with the disease at a younger age. In later life, however, rates are higher in men. 

The difference in trends is likely driven by younger women spending more time in the sun or on sunbeds for tanning purposes, says Cancer Research UK. Older men, meanwhile, often know less about the dangers of sun exposure.

Overdiagnosis - where cases that otherwise wouldn't cause harm are flagged - could also be contributing to rising rates of the cancer, say experts. 

With temperatures expected to reach as high as 30C in parts of the UK over the bank holiday weekend, the charity is urging people to cover up and use sunscreen to minimise their risk.

Cancer Research UK's chief executive, Michelle Mitchell, said it was 'concerning' to see the number of people being diagnosed with the deadly disease. 

'The fact that most of these cases are preventable underlines the importance of people taking sun safety seriously,' she said.  

The latest figures mark the first time that melanoma cases in the UK have risen above 20,000. Research shows that as many as 18,000 of these are preventable. 

Almost 90 per cent of melanoma is caused by too much exposure to ultra-violet (UV) light, either from the sun or sun beds, which can damage the skin's DNA.

Other factors believed to contribute to the rise in cases include an ageing population and better awareness of the warning signs of skin cancer.

Despite the spike in diagnoses, deaths from melanoma are expected to fall, the charity says. 

Vital improvements in early diagnosis and treatment are helping patients with skin cancer live longer, with almost nine in 10 adults diagnosed with the disease in England now surviving 10 years or more. 

'Sunburn is a clear sign your skin has been damaged,' says Fiona Osgun, head of health information at Cancer Research UK.

'Sunburn doesn't only happen when it's hot - it can happen on cooler, cloudier days too,' she added. 

Getting sunburned just once every two years can triple the risk of developing skin cancer, studies have shown.

'The best way to protect your skin when the sun is strong is to use shade, particularly in the middle of the day, cover up, especially your shoulders, and wear a hat and sunglasses and finally, wear sunscreen, with at least SPF 30 and four or five stars,' says Ms Osgun. 

'Make sure you put plenty on and reapply it regularly. Even if you've been sunburned before, it's never too late to start protecting your skin.'

With warmer weather fast approaching, the charity is urging people to spend time in the shade - particularly when UV index is highest, between 11am and 3pm - to cover up, and regularly apply sunscreen.

When diagnosing melanoma, doctors typically use a checklist known as the ABCDEs.

This includes asymmetry, border, colour, diameter and evolving moles as tell-tale warning signs for the disease.

However, not all of these changes confirm melanoma. 

As such, Professor Peter Johnson, National Clinical Director for Cancer at NHS England, said: 'If you notice anything unusual like a new mole, a changing lesion or any patch of skin that doesn't look right then please don't wait to contact your GP because catching cancer early really does save lives.

'Melanoma skin cancer is one of the most preventable cancers and these figures are a stark reminder of the importance of staying safe in the sun.

'With sunny weather forecast this Bank Holiday, we want people to enjoy the sunshine sensibly by using high-factor sunscreen, covering up and seeking shade – especially during the hottest parts of the day.'