Almost half of all flights at Heathrow in the first three months of the year were delayed, according to statistics released yesterday by the Civil Aviation Authority (CAA).

The figures show that just 56% of flights at the airport left early or within 15 minutes of the scheduled departure time – the measure the CAA uses to define an on-time departure. In the same period in 2007, two thirds of flights left on time.

Passengers passing through Heathrow experienced an average delay of 25 minutes.

The period includes the botched opening of the new Terminal 5 at the end of March. However, the figures for March are actually better than for January and February, largely because the figures do not take account of cancellations. British Airways cancelled large numbers of short-haul flights from the airport on 27 March and in the days that followed in a bid to reduce delays.

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Heathrow’s delays were worst in January, when just 50.6% of flights were on time and the average delay was nearly half an hour. Many delays were caused by the crash landing of a British Airways’ Boeing 777 jet at the airport, causing the closure of one of Heathrow’s busy runways and delaying hundreds of flights.

The delays are the worst at the airport in recent memory. Even in September 2001, when many flights were delayed because of the World Trade Center attacks, 64.7% of flights from the airport were on time.

An airport spokesperson said: “The CAA's figures are the latest evidence of the problems caused by a lack of capacity at Heathrow Airport. Heathrow's two runways are operating at 100% of capacity, which means small events such as adverse weather, can cause major delays and disruption. Other airports, which have plenty of spare runway capacity, do not suffer these problems."

The CAA figures also show that Stansted is the UK airport where you are least likely to be delayed - 80% of flights from there leave on time and the average delay is just 11 minutes.