The figure comes from the Intensive Care National Audit and Research Centre (ICNARC) and is based on a sample of 3,883 coronavirus patients.
It comes as the UK saw its deadliest day in the outbreak so far with a record increase of 980 deaths in just 24 hours, pushing the total fatalities up to almost 9,000.
The recent study shows that out of 1,689 patients in the sample whose care outcome was known, 871 died (51.6 per cent), while 818 were discharged.
In comparison, just 22 per cent out of 5,367 patients taken into critical care with non-Covid-19 viral pneumonia died between 2017 and 2019.
The coronavirus figures come from 284 NHS critical care units in England, Wales and Northern Ireland taking part in an ICNARC programme as of 4pm on April 9.
According to the study, the data shows that: "Of the 3,883 patients, 871 patients have died, 818 patients have been discharged alive from critical care and 2,194 patients were last reported as still receiving critical care."
The mortality rate is currently higher for men and increases with age, the data shows.
Of the 871 people who died, 53.6 per cent were male, while 46.3 per cent were women.
Meanwhile, the largest number of deaths were among those aged between 70-79 at 298, followed by the 60-69 age group, with 273 reported.
Thirty-one patients died aged between 16-39, 46 were 40-49 and 145 were 50-59. A total of 78 patients died aged over 80.
The average (mean) age of those admitted to intensive care with coronavirus was 59.8 years, with 72.5 per cent of patients recorded as male.
Some 2,291 (59 per cent) patients in critical care had to be mechanically ventilated in the first 24 hours, the study revealed.
The largest number of Covid-19 patients remains in London, with 1,428 being managed by the three London Operational Delivery Networks - the system of co-ordinating patient care across the capital.
Previous figures from April 3, recorded the death rate as being at 50.1 per cent.
Critical care units involved in the initiative are asked to notify ICNARC as soon as they have an admission with Covid-19 and provide data at different points of their treatment.