Pregnant women and pensioners have been forced to stand in "chaotic" queues at Heathrow Airport for four hours.
The Home Office has blamed the huge waits at border control on understaffing.
A spokesman for the department previously said travellers "needed to accept" delays due to the summer holiday demand and the requirement to check Covid documents.
However, passengers are fuming about the scandal, with former Tory leader Iain Duncan-Smith warning that the crowded airport terminals could even lead to the spread of coronavirus.
He told MailOnline: "We are going to achieve the worst of all worlds by having people close together who may have Covid.
"The whole thing is chaotic and we still haven't fully opened up yet. We don't seem to have a plan for how we are going to manage that.
"'If it carries on like this Heathrow will cease to be a hub airport and Britain will be left in the backwash as an irrelevant country."
Mr Duncan-Smith said the UK needed to "get on with things" and end the "madness" as the majority of the population have now been jabbed.
Tory MP James Gray said it was "deeply embarrassing" that the UK could not "get people into Britain faster".
He now wants a review of Border Force and for officials to face the select committee.
The chaos reportedly started on Sunday and has continued every day this week.
People claimed e-gates "stood empty" as they queued up to get through passport control.
One passenger tweeted yesterday: "Chaos at Heathrow Airport Terminal 4. Four hours waiting to go through immigration.
"Families with children, pregnant ladies and old folks everyone had to wait. Is that human?"
Another said there was similar chaos at Terminal 5 yesterday, with empty e-gates and families forced to queue for more than an hour if they had children aged under 12.
Youngsters under 12-years-old cannot use e-gates due to facial recognition technology limitations, Mail Online reports.
The situation at the airport was compared to scenes from the final days of the Soviet Union by journalist Guy Faulconbridge.
Earlier this week, a Home Office spokesman told MailOnline: "Our utmost priority is protecting the safety and health of the public and we will never compromise on security, and on ensuring passengers are compliant with the current health measures, which means passengers will need to accept an increase in the time taken to cross the border.
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"The rollout of upgrades to our eGates to automate checks for health requirements is ongoing, with many eGates already in operation and more to be added over the coming months to increase automated checks on passengers at airports.
"However, for safeguarding reasons families with children under the age of 12 are not permitted to use the eGates.
"Where there are high volumes of families with young children, such as over the summer holidays, Border Force may dynamically deploy resources to frontline desks instead and we continue to flexibly deploy our staff to make the process as smooth as possible."
