New figures show that the Border Force failed to meet its targets for getting non-EU passport holders through immigration at Heathrow last month.
The agency aims to get 95 percent of passengers through within 45 minutes, but at Terminal 5 they only managed 76 percent.
The figures were released on BAA's website after the Government admitted the Border Force needs to change the way it operates. Large queues built up at passport control at the airport last week, with some passengers waiting for up to three hours.
However, the Border Force did meet its targets for EU passport holders, meaning that 95 percent of passengers were processed in less than 25 minutes.
Terminal-by-terminal figures at Heathrow in April 2012 - percentage of non-EU passport holders processed within 45 minutes:
Terminal 1 - 94.5%
Terminal 3 - 87.0%
Terminal 4 - 84.4%
Terminal 5 - 75.7%