Passengers at Heathrow have told of their frustration, after facing long queues at Terminal 5's border control.
Some say they waited up to three hours.
The UK Border Force insists it is fully prepared for the Olympics, but with just 90 days to go, there are fears the airport may not cope.
Now, Immigration Minister Damian Green is to be grilled by MPs on the issue.
Ria Chatterjee reports.