Regulators have called into question the way the UK's two biggest airports have been measuring the length of their security queues.

Month-long independent checks at Heathrow and Gatwick showed longer queues for passengers than the airports had reported in previous months, the Civil Aviation Authority said.

Bosses at Heathrow had to make a penalty payment totalling £500,000 after the audit found a higher proportion of passengers queued for longer than five minutes in July 2011 at Terminal 5 than in previous months.