Deaths in England, Wales and Spain are more than a third higher than normal, scientists studying the pandemic claimed.
The three countries have the largest number of excess deaths caused by coronavirus, compared with other nations that introduced earlier lockdowns and have better healthcare systems, according to a study by Imperial College London.
The results, published on Wednesday by the journal Nature Medicine, came as UK Prime Minister Boris Johnson faced pressure to reintroduce a national lockdown to save lives.
Dr Oliver Watson, from Imperial College London, said the research shows early action has a significant effect on infection rates.
“Timing of policies, whether lockdowns or ability to scale up testing quickly, have been the real drivers of excess mortality,” he said.
Mr Johnson launched a three-tier traffic light system in England on Wednesday, which will mean only regions with the highest infection rates face tougher measures, amid warnings that the National Health Service may soon be overwhelmed.
Despite ignoring his leading scientists’ advice to introduce an immediate lockdown, he has not ruled out a two-week lockdown as a circuit breaker.
"The whole point is to seize this moment now to avoid the misery of another national lockdown," Mr Johnson said.
"We're going to do it – and I rule out nothing, of course, in combating the virus – but we are going to do it with the local, the regional, approach that can drive down and will drive down the virus if it is properly implemented."
On Wednesday, Northern Ireland, which is outside the tier system, announced the toughest UK coronavirus measures since the pre-summer peak, shutting restaurants and suspending schools.
The Netherlands has also introduced a four-week lockdown to combat rising numbers.
In the latest research, scientists found a comparison of 21 developed countries during the start of the pandemic shows that those with early lockdowns and well-prepared national health systems avoided large numbers of additional deaths as a result of the outbreak.
Researchers used the number of weekly deaths in 19 European countries, New Zealand and Australia over the past decade to estimate how many people would have died from mid-February to May 2020 had the pandemic not happened.
The authors, led by Prof Majid Ezzati of Imperial College London, then compared the predicted number of deaths with the reported figure during that period to determine how many probably occurred as a result of the pandemic.
The study found there were about 206,000 excess deaths across the 21 countries during the period.
Spain topped the list with a 38 per cent increase in expected fatalities, followed by 37 per cent in England and Wales.
Italy, Scotland and Belgium also had significant excess deaths, while in Hungary, Denmark and Australia there was no marked change and in Bulgaria there was a decrease.
The authors found the different governments’ efforts to suppress transmission of the virus and the ability of their national health systems to cope with the pandemic played a major role.
“What puts England, Wales and Spain as doing worse than other countries is this combination of long and intense – long period of impact and quite large rises,” Prof Ezzati said.
Dr Amitava Banerjee, a professor of clinical data science at University College London, said measures including lockdowns, protecting high-risk groups and establishing effective test, trace and isolate systems were necessary.
“Even if vaccines and better treatments for severe Covid-19 infections are developed, the way to minimise excess deaths is to reduce the infection rate through population level measures,” he said.
On Wednesday, the US still had the highest number of coronavirus deaths in the world with 215,955.
The UK had the fifth highest with 43,108, followed by Italy with 36,246 while Spain was the eighth worst with 33,204.
