Professor Sir David Spiegelhalter, a statistician at the University of Cambridge, said the spike was "incredibly vivid".

"I don't think I've ever been as shocked when I've looked at something, particularly as just over half of that spike were death certificates with Covid written on them," he said.

"We knew there was going to be a pump in Covid-registered deaths. I hadn't expected such a huge number of deaths which didn't mention it on the death certificate."

The unexplained deaths are likely to be related to Covid-19 but have not yet been detected, such as deaths in care homes, where many residents die before a doctor can examine them, or deaths from unrelated illnesses.

Care England data recently suggested as many as 7,500 could have died from coronavirus in care homes so far.

A similar scenario is playing out in Scotland and Northern Ireland.

As death registration is a faster process in Scotland, more recent data is available. And more excess deaths are beginning to be associated with Covid-19.

In week 14 coronavirus deaths equated to around 46 per cent of all excess deaths. By week 15 it was almost 70 per cent, and in week 16, 77 per cent.

Prof Sir David Spiegelhalter said it is possible doctors are becoming more confident including Covid-19 on the death certificate.

"There is a demonstrable, statistically significant number of excess deaths that have not got Covid on the death certificate," he said.

"Perhaps we have elderly people not showing classic Covid symptoms, but for whom even a mild form of the disease is sufficient for them to succumb.

"Perhaps a doctor did not feel the symptoms were sufficient to be confident labelling it as Covid. This could be because doctors are becoming more confident at putting suspected Covid on death certificates.

"The other worrying factor is how many of those deaths are in fact people who have not got Covid but we might consider collateral damage - not attending hospital for their underlying condition, either because they feel they do not want to burden the hospital or they regard it as a risky place to be."

Tom Dening, a professor of dementia research at the University of Nottingham, said: "There are probably multiple reasons for other deaths. These include people not feeling able to attend their GP surgeries, call an ambulance or attend A&E as they may have done in the past. Therefore, some serious conditions may present too late for effective treatment.”

"Another possibility is that some people with serious conditions, like cancer or chronic kidney disease, are either unable or unwilling to attend hospital on the usual regular basis, so their treatment regimes may lapse."

It follows the release of NHS figures which showed that, since the beginning of the outbreak, A&E attendance has dropped to its lowest level since modern records began.

Shifting deaths from hospital to the home

The number of deaths in care homes in England and Wales have tripled in three weeks, according to the latest ONS data.