A charity has expressed concerns for the mental health of tens of thousands of cancer patients who are feared to be scouring the web for answers about their diagnosis.

More than a quarter of a million people with cancer in Britain may have been left feeling anxious, depressed or confused after looking for information online, Macmillan Cancer Support said.

Some 39% of cancer patients surveyed for the charity said they had looked online for information about their diagnosis, of which more than a quarter (27%) reported a detrimental impact.

This rises to two in five (39%) of those who turned to the internet within moments of their diagnosis, the YouGov survey of 2,004 adults found.

Overall, one in 10 of the cancer patients (11%) said they had been negatively affected by looking up their diagnosis online.

When the results are scaled up to reflect the UK cancer population, it suggests more than 300,000 people could have experienced similar feelings.

Issuing a stark warning, Macmillan said people were turning to the web because they are confused about what their diagnosis means, with understaffing and unmanageable workloads hindering frontline staff.

Dr Rosie Loftus, chief medical officer at Macmillan Cancer Support said: “In today’s digital society, it is understandable that people look up their diagnosis online when they’re told they have cancer.

“However, it is extremely concerning that such a high number of people who turn to the internet for support are presented with such a seemingly negative outlook.

“It is vital people with cancer are supported from day one. This not only depends on the cancer workforce having the time and capacity to fully explain what a diagnosis means, but also signposting people to reputable sources to ensure they start their cancer experience on the right foot.”

The top reasons for looking up their condition were to look for more information and to find out about their prognosis, Macmillan said.

Five per cent of the respondents said they had found bogus cancer cures online, while 5% said they thought they were going to die after searching the web.

Extrapolated to the UK cancer population, this could be more than 50,000 people for each scenario, Macmillan said.

Professor Peter Johnson, NHS clinical director for cancer, said: “Going online is a quick and popular way to find information, but it is vital that internet and social media platforms help people find reliable sources of information, and not those promoting myths and ‘miracle cures’ which at best don’t help, and at worst put people’s lives at risk.

“As part of our long-term plan we are rolling out a faster diagnosis standard so that people get certainty sooner, and investing in more clinical nurse specialists and other professionals to ensure people get more personalised cancer care, including information they can trust.”