The number of night flights in and out of Heathrow airport has exceeded government targets.
Night flights should average 16 a night at Heathrow during the winter
In the six months to March 2007 there were 109 more flights than the 2,550 quota, set by the Department for Transport (DfT) last year.
This is allowed due to a 10% flexibility for operational reasons.
But figures, seen by BBC London, show there were a further 325 "disregarded flights". The DfT said this was due to circumstances, like poor weather.
Heathrow in west London is allowed 2,550 take-offs and landings to take place between 2330 and 0600 during the six-month "winter season". In the summer months this rises to 3,250.
These quotas have been set until 2012.
Some local residents under the flight path in south and west London have complained about the flight noise at night.
Patricia Nicholson said: "We were relieved when the government promised to cut night flights for the next six years.
"But it is very disappointing they have been bringing in extras flights seemingly by stealth.
"A lack of sleep is difficult to tolerate."
Aviation Minister Jim Fitzpatrick said: "In exceptional circumstances, the airport has the power to disregard night flights from the movements and quota limits, set by the Secretary of State.
"For example, when security alerts, severe weather conditions or prolonged air traffic control disruption could lead to delays likely to cause serious hardship or suffering to passengers."
He added the DfT would examine the figures to make sure the aviation industry is adhering to them.
BAA said the extra flights were due to heavy fog in December 2006, when more than 300 flights were cancelled.