Passengers at Heathrow airport's glittering new terminal, which opens three months from today, will face a tough new zero-tolerance policy: be in the queue for security at least 35 minutes before the flight or count as a "no show".

British Airways, the sole tenant at Terminal 5, is seeking to improve its woeful punctuality. Even without the kind of disruption seen at Heathrow and Gatwick before Christmas, BA's operations routinely fail the airline's own modest targets. For the week ending 16 December, fewer than one in three flights departed on time, compared with a target of 52 per cent.

It is believed to be the first time, at any airport, that an airline has taken such a hard line on passengers who have already checked in. The only exception to the 35-minute rule will be travellers on standby, who get an extra five minutes' grace to allow for the fact that their seats are assigned only after check-in formally closes at "minus 45".