Almost 100,000 Britons are at risk of dying because they do not know that they have the deadly liver disease hepatitis C, health officials are warning.

An estimated 95,600 people in the UK, mainly drug users, are believed to be suffering from the disease but are unaware of the condition because they have not been diagnosed, said Public Health England (PHE) on Friday.

Steve Mowle, of the Royal College of GPs, said: “It’s extremely concerning to hear that so many people have undiagnosed hepatitis C. It’s a dangerous disease for individual patients and a significant public health risk.”

Nine in 10 people infected with the hepatitis C virus (HCV) inject recreational drugs such as heroin or have done so, according to a new PHE report on the condition. The virus is spread among drug users by sharing contaminated needles.

Although heroin use by injection is declining, drug users in some parts of England are injecting other substances – such as stimulants, cocaine and crack – PHE has found. “These are associated with more frequent injection, more damage at the injection site and with the spread of viral and bacterial infection,” its report adds.

This is the first time that PHE has put a figure on the number of undiagnosed hepatitis C sufferers. Its estimate was based on anonymous health monitoring of people who inject drugs. It urged anyone who might be at risk to get tested before their health was affected.

The undiagnosed 95,600 people with the liver disease are at increased risk of dying because hepatitis C can kill if left untreated. The 95,600 represent about two-thirds of the 143,000 people whom PHE estimates have the disease, meaning the undiagnosed outnumber those known to have it by two to one. Overall numbers are in decline, though. Those 143,000 are down on the 182,400 who were thought to have it as recently as 2015.

The number of deaths from HCV-related liver disease has fallen in recent years but it still claimed 380 lives last year. However, that was 19% fewer than the 468 recorded in 2015. In 2017, 63 people with advanced liver disease due to HCV had a liver transplant to save their lives.

Helen Harris, a senior scientist at PHE, said: “HCV is a blood-borne virus that can cause life-threatening liver disease, including cancer. However, those infected often have no symptoms until decades later, when their liver has been badly damaged.” Symptoms, which include flu-like illness, loss of appetite and tiredness, are often mistaken for evidence of other conditions.

Harris added: “Hepatitis C can have devastating consequences but most cases can be cured if detected in time, which is why it’s so important to find and treat those who may be infected.”

The recent development of new drug therapies means that 95% of sufferers who take those treatments are cured.

Pamela Healy, chief executive of the British Liver Trust, said: “There is now an effective cure for everyone living with hepatitis C and ... the numbers of people living with HCV are going down. The challenge now is for us to find the tens of thousands – an alarming amount – who are currently undiagnosed.

“If you have ever dabbled with drugs, even when you were much younger, practised unsafe sex or had a tattoo while travelling abroad, please get yourself tested just to make sure.”