Travellers have been released from quarantine hotels after the Government scrapped the red list.
The PA news agency understands they were told they could leave from 4pm, some 12 hours after the requirement to self-isolate in a hotel was dropped for new arrivals.
It has been reported that some travellers left their accommodation before then.
Only those who have received a negative result from a coronavirus test result were allowed to leave.
Health Secretary Sajid Javid said released travellers “will get a refund for the portion of the space that they booked that they have not used”.
People with a positive result, or those who are not fully vaccinated and are a contact of someone with a positive result, must remain in quarantine.
Concern over the Omicron coronavirus variant led to 11 African countries such as South Africa, Nigeria and Zambia being put on the red list.
People arriving in the UK from those locations were required to spend 11 nights in a quarantine hotel at a cost of £2,285 for solo travellers.
But Mr Javid announced on Tuesday that the list would be axed as the prevalence of the strain in the UK meant it was “now less effective in slowing the incursion of Omicron from abroad”.
Jonathan Mogford, who is responsible for the managed quarantine service at the UK Health Security Agency (UKHSA), told the Commons Transport Committee on Wednesday that there have been “unprecedentedly high rates” of positive Covid cases among red list travellers.
He said latest figures suggest “nearly 5% of people in the hotels are positive”.
There have been “roughly 5,000 guests through in this round of red listing”, he said.
His comments indicate that around 250 of those people tested positive.
UKHSA chief executive Dr Jenny Harries said travel restrictions have “a time and place” in protecting public health.
She told MPs that the red list was deployed “as a delaying tactic”, giving the UK “time to prepare” for the Omicron variant.
But now that the strain’s rate of growth in the UK is “significant”, it is “really important” that country-specific restrictions are lifted, Dr Harries said.
Travellers entering the UK must take a pre-departure test and self-isolate until they receive a negative result from a post-arrival test.
Committee members and Labour former cabinet minister Ben Bradshaw claimed Transport Secretary Grant Shapps told him the travel testing regime was “pointless”.
He said: “The health minister said to me in the House yesterday that he thought they were pointless and the Transport Secretary told me in the division lobby last night that he thought they were pointless too.
“Someone is obviously keeping them in place, who is keeping them in place?”
Dr Harries replied: “It’s not for us to make decisions. We give advice to ministers and I can’t speak on behalf of either of the ministers that you have just mentioned.”
Downing Street insisted the measures were not “pointless”.
The testing requirements “remain important in helping to prevent additional Omicron from seeding in the United Kingdom”, the Prime Minister’s official spokesman said.