About half will be leaving on package holidays; others to visit friends and relatives.
Keith Betton, head of corporate affairs at Abta, said: 'It's going to be very, very busy indeed. This year the number of people travelling away is bigger than previous years.'
More than 650,000 passengers are expected to pass through London's Heathrow airport in the next five days - 3.5 per cent up on last year - but that figure includes Britons flying home, business passengers and those passing through in transit.
Mr Betton said that a combination of increased optimism and good price deals was responsible for the Christmas boom. 'It's like unblocking a dam . . . a lot of people have not been on holiday for a while and are making up for it now.'
The most popular destinations are the Canary Islands, Cyprus, Tunisia and the Gambia in West Africa. Florida was also a favourite but many were also getting away for just a few days to Paris or Amsterdam.