Covid cases have fallen for a sixth day in a row, with scientists saying a combination of vaccines, the "pingemic", school holidays and good weather may be responsible.

The daily reported infections for Monday stood at 24,940 – a drop of 14 per cent since Sunday and down 15,000 since the same time last week.

Figures suggest all regions are now seeing declines, with big decreases in previously high areas such as the north east of England, where daily cases have fallen by two thirds since the peak on July 15.

Scientists said they were puzzled by the sudden steep drop, which has come after more than six weeks of worrying rises. Experts said the downturn may be caused by more people being vaccinated along with the good weather, which has enabled people to socialise outdoors.

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"There are certainly multiple factors at play here," said Adam Finn, professor of paediatrics at the University of Bristol. "These include infection-induced immunity, vaccine-induced immunity and, critically, behaviour. 

"With every passing day, another cohort of people, recently immunised, is added to our protection alongside those who have recently had the infection, survived and recovered."

Others believe the pingdemic may be preventing transmission because so many people are now self-isolating. The school holidays also mean testing is no longer being carried out in schools, so it is also possible that asymptomatic cases that were previously picked up are now being missed.

Scientists warned that there was also a five per cent drop in tests last week, which may have skewed the figures, and said it was still too soon to see the impact of the full release of Covid restrictions on July 19.

Dr Stephen Griffin, an associate professor in the school of medicine at the University of Leeds, said: "The recent fall in cases in England is great news, but also puzzling given that progressive relaxation of restrictions has occurred, with the final release of all measures last week.

"I would be surprised if we are likely to see a continuation of this decline."

Map of UK’s seven-day Covid-19 infection rate, by local authority

The falls come despite modelling which suggested the summer peak in Britain would hit 100,000 to 250,000 a day. It now appears the third wave peaked at 56,000 daily infections on July 15, way below forecasts. If the downward trend continues, deaths and hospital admissions are likely to start falling within the next fortnight.

By July 22, the last data available, there were 5,000 Covid patients on Britain’s wards – just 15 per cent of the previous peak, when they reached nearly 40,000. Deaths are also currently well below previous waves, with 28 recorded on Sunday compared to daily peaks of more than 1,000 per day. 

Prof James Naismith, of the University of Oxford and the director of the Rosalind Franklin Institute, said: "Many scientists, myself included, expect the end of lockdown to see a rise in cases. However, we have been wrong before and we will be wrong in the future. Only charlatans claim omniscience."

Boris Johnson’s official spokesman warned that the country was “not out of the woods yet” and needed to brace for a possible surge in cases as a result of last week’s unlocking.

"We have said last week when we moved to step four that allowing large numbers of people to meet in indoor settings would have an impact on case numbers, and it remains the case that we won’t have seen the impact of step four yet in terms of case numbers," he said. "We will continue to keep all the stats under review."