Four in five Britons infected with hepatitis B do not even know they have it, a study warned.
It is estimated 0.7 per cent of the UK population or around 441,000, have the virus which can cause deadly hepatitis-B-related liver disease.
It is highly contagious and mainly transmitted from infected mothers to their babies, through unprotected sex or contaminated needles.
Yet despite a test being available since the 1970s just a fifth of infected Britons have been diagnosed.
Hepatitis B is an infection of the liver caused by a virus that's spread through blood and body fluids and often doesn't cause any obvious symptoms in adults who recover in months.
But in children it often persists for years and may eventually cause serious liver damage.
It is less common in the UK than other parts of the world, but people originally from high-risk countries, drug users and those who have unprotected sex with multiple sexual partners are most at risk.
The NHS offers vaccines to those most at risk of infection and to all babies born after August 2017 in the UK.
The scale of infections in Britain were revealed in the most detailed analysis of national, regional, and global prevalence.
It found globally nine in ten of those infected were undiagnosed and around 300 million people were living with hepatitis B virus (HBV).
Yet just one in 20 (5%) eligible patients are getting treatment.
And despite vaccine programmes half of babies worldwide still do not receive life-saving vaccine at birth.
Moreover, less than 1 per cent of HBV-infected pregnant women who are at high risk of passing the virus on to their children and are the main source of the ongoing epidemic, are receiving the appropriate treatment.
Scientists from the Polaris Observatory at the Centre for Disease Analysis Foundation, Lafayette, in the US warn the WHO targets toward elimination of HBV are unlikely to be achieved by 2030 without a rapid scale-up in access to screening and treatment in most countries.
The research analysed 435 studies and 620 national experts to calculated the prevalence of HBV infection globally.
The virus is most common in east Asia and sub-Saharan Africa, where prevalence is as high as 12.1% in Central African Republic compared to 0.7% in the UK.
In 2016, 21 countries accounted for more than 80% of all HBV infections, with China, India, Nigeria, Indonesia, and the Philippines accounting for over 57% of all infections
Furthermore it calculated just five per cent or 4.8 million of 96 million of those suitable for treatment received antiviral therapy in 2016.
In Western Europe, the proportion of eligible patients receiving treatment ranged from three per cent (480) in Belgium, and five per cent in Ireland (60), Norway (220), and Portugal (1800), to 95% (2,700) in Finland.
In the UK, only a quarter or 27,900 of those eligible had received treatment in 2016.
A vaccine against HBV became available in 1981 and since 1992 WHO has recommended all newborns receive their first dose within 24 hours of birth.
Babies born to HBV-infected mothers should also be given protective antibodies known as hepatitis B immunoglobulin (HBIG).
The authors noted in 2017, the UK and Norway became two of the last countries in Europe to offer the vaccine to newborns.
Dr Homie Razavi said: "Most mother-to-child transmission occurs within days of birth, so the birth dose is vita
"All children need to receive this life-saving vaccine at birth, not just half of them."
Of the 16 countries that account for more than 80% of infections among five-year-olds, only China has scaled-up timely birth-dose coverage to 90%.
What's more, 10 of these countries have yet to introduce universal timely birth dose vaccination. F
For example, in Pakistan birth dose and HBIG are only available in the private sector.
Dr Razavi added: "We have all the tools necessary to eliminate HBV.
"Our estimates highlight an enormous opportunity for effective screening, diagnosis, and treatment to substantially reduce the numbers of new infections in all countries by 2030.
"But we must accelerate efforts across the board.
"We hope this work will be the catalyst to support national strategies to eliminate the virus by 2030 - which 194 countries have pledged to do."
The study was published in The Lancet Gastroenterology & Hepatology.