The UK made 'serious mistake' by not getting travellers to quarantine in early days of pandemic, a damning report has found.
The government has been accused of being 'too slow' in closing the borders which possibly 'accelerated' the spread of coronavirus.
The Home Affairs committee, made up of a group of MPs, said that ministers had underestimated the threat of importing the virus from Europe as opposed to Asia where the virus is believed to have started.
It adds that allowing millions of people to enter the UK from growing Covid-19 hotspots could have lead to tens of thousands of infections in March.
But the government says that the Home Affairs select committee are "incorrect in their assertions".
The report found that if stricter rules had been put in place during the spring, fewer infections would have entered the UK - which is now among the worst affected by the virus.
In its report, the committee also referenced a study which indicated more than 1,300 separate strains of the virus were imported largely from Spain, Italy and France during that early period.
The committee chair, Yvette Cooper, said: "The Government's failure to have proper quarantine measures in place in March as the infection was spreading fast was a grave error and meant Covid spread faster and reached more people.
"The UK was almost unique in having no border checks or quarantine arrangements at that time. That alone should have rung loud alarm bells for ministers and made them think again."
The select committee said that it was an "inexplicable decision" to lift restrictions on March 13 on people coming from high-risk countries to self-isolate at home.
The report concluded it was a "serious error".
A government spokesperson said: "The Home Affairs Select Committee are incorrect in their assertions.
"All of our decisions throughout the pandemic have been guided by the science, with appropriate measures introduced at the right time to keep us all safe.
"And with passengers numbers significantly reduced, the scientific advice was clear that quarantine measures for those entering the country from abroad would be most effective when the UK has a lower level of infection.
"Therefore, as the virus was brought under control here, border measures were introduced on 8 June to protect public health and help avoid a second peak that would overwhelm the NHS."
