The UK coronavirus death toll is expected to continue to rise for at least two weeks, the government’s chief scientific adviser has said, despite encouraging signs about the rate of infections and hospital admissions.

Sir Patrick Vallance told Thursday’s daily Downing Street briefing that the number of people to have died from coronavirus in UK hospitals had reached 7,978, after the deaths of a further 881 people. It is the second-highest daily total after Wednesday’s record 938 deaths.

Despite the slightly lower figure, Vallance said the peak of the outbreak could still be weeks away. “I would expect the deaths to continue to keep going up for about two weeks after the intensive care picture improves. We’re not there yet, but that’s the sort of timeframe I would expect.”

The chief medical officer for England, Prof Chris Whitty, pointed out that two weeks ago admissions to intensive care were doubling every three days. He said: “It’s now becoming not quite flat, but doubling time is now six or more days in almost every area in the country. That has only happened because of what everybody has done in terms of staying at home.”

The official UK figure of 881 new deaths differs from the 891 total from figures released separately by agencies in the UK’s four countries, which gather their data differently. NHS England said a further 765 people had died, ranging in age from 24 to 103. Only 43 of those patients had no known underlying health condition.

Scotland recorded 81 deaths, taking its total to 447. Unlike the rest of the UK, Scotland’s total includes some deaths outside hospitals because it counts all fatalities where Covid-19 is recorded as a cause on a death certificate.

Wales recorded 41 deaths, taking its total to 286; and in Northern Ireland there were four more deaths, taking its total to 82.

Play Video 4:41 Why are coronavirus mortality rates so different? – video explainer

Last week the health secretary, Matt Hancock, said the NHS was preparing for at least 1,000 deaths a day, at a time when scientific advisers were forecasting the outbreak to peak at Easter.

The peak was now expected to come in four weeks, after signs that the transmission rate was beginning to fall. New infections continue to fluctuate. On Thursday, 4,344 new cases were recorded, compared with 5,492 on Wednesday, but the day-on-day rise was still higher than three of the previous four days.

James Naismith, a professor of structural biology at the University of Oxford, said: “It is a mercy that the number of deaths reported today is lower than yesterday but on its own, a single day’s number is of no value in judging the pandemic. The continuing volatility in daily figure of announced deaths [due to different reporting periods and delays] makes it almost impossible to identify any trend with certainty yet.”

He added: “If deaths are still following a rapid exponential growth, today’s new deaths would have been expected to be markedly higher than yesterday’s, and the total number of deaths to date would have doubled from that four days ago. Most, if not all, the deaths reported today will have come from infections before the so-called ‘hard lockdown’. It does seem that the hard lockdown is, as expected, reducing the rate of increase in the number of new hospital admissions.”