The 26 richest billionaires in the world own as many assets as the 3.8 billion people who make up the poorest half of the planet's population. Do we live in a fair world? That is the question being posed by the charity Oxfam.

Its annual wealth report was released on Monday to coincide with the World Economic Forum in Davos. It says billionaires' fortunes increased by 12 percent last year – or $2.5 billion a day – while 3.8 billion people making up the poorest half of the world's population saw their wealth decrease by 11 percent.

Titled "Public Good or Private Wealth", the report reveals the growing gap between rich and poor and how it is undermining the fight against poverty, damaging world economies and fuelling public anger across the globe.

"The size of your bank account should not dictate how many years your children spend in school, or how long you live – yet this is the reality in too many countries across the globe," said Oxfam International's Executive Director Winnie Byanyima. "While corporations and the super-rich enjoy low tax bills, millions of girls are denied a decent education and women are dying for lack of maternity care."

The report highlights how the number of billionaires has almost doubled since the financial crisis, with a new billionaire created every two days between 2017 and 2018, yet wealthy individuals and corporations are paying lower rates of tax than they have in decades.

Oxfam said that a one percent wealth tax would raise an estimated $418 billion a year – enough to educate every child not in school and provide healthcare that would prevent three million deaths.

Once taxes on consumption such as VAT are taken into account, the report said, the poorest 10 percent of Britons are paying a higher effective tax rate than the richest 10 percent (49 percent compared with 34 percent).

Oxfam has produced similar reports for the past four years. It shows the number of billionaires owning as much wealth as half the world's population fell from 43 in 2017 to 26 last year. The number was 61 in 2016.

The charity said figures on the share of wealth owned by the poorest half of the population come from Credit Suisse Wealth Databook and relate to the period June 2017 – June 2018. Figures on the very richest in society are based on more detailed data from the annual Forbes Billionaires List and relates to the period March 2017 – March 2018.