The drug, according to reports, was initially intended for use on Ebola victims.
Clinical trials suggest remdesivir can shorten recovery time for Covid-19 sufferers by an average of four days, from 15 to 11.
Formal licence approval takes months but the Medicines and Healthcare products Regulatory Agency said the anti-viral drug can be prescribed before this is complete.
Hospital doctors can give remdesivir to Covid-19 patients aged over 12, while clinical trials with manufacturer Gilead Sciences continue, Mirror UK reports.
The move boosts efforts to find an effective treatment and improve NHS capacity to cope with a potential second wave of the disease.
Health Secretary Matt Hancock told the daily Downing Street briefing: “This is probably the biggest step forward in the treatment of coronavirus since the crisis began.
“These are very early steps but we are determined to support the science and back the projects that show promise.”
He spoke as daily deaths in the UK fell to 134, the lowest for six weeks. And there were no new deaths in Northern Ireland for the first time since the pandemic started. Department of Health data put the full toll at 37,048.
But 47,300 coronavirus deaths have been officially recorded once Office for National Statistics data where Covid-19 is mentioned on death certificates is combined with NHS England data on deaths following a positive test.
The news on remdesivir comes after a hospital in Weston-super-Mare had to stop taking in patients over the bank holiday when it hit maximum capacity amid an influx of Covid-19 cases.
