The UK Border Agency missed its April targets for passport checks at Heathrow Airport, falling short at each terminal, according to BAA.
The figures, available on the BAA website, show that percentage targets for getting non-EU passport holders through immigration in under 45 minutes fell short by as much as 20% in some terminals.
The target number is 95% but the newest terminal, Terminal 5, was only able to pass 75.7% of incoming passengers through within the 45-minute target.
Terminal 1 only fell shy by 0.5% while 3 missed by eight percentage points and Terminal 4 by 10.6%.
The statistics come at a time when the government is attempting to change the way the Border Force operates.
However, the changes to the system introduced by the Home Secretary Theresa May have not been universally welcomed with Brodie Clark, former head of the UK Border Force, claiming last month that the current methods have reduced frontline staff to "box-tickers and rule followers".