Almost a quarter of all bmi's summer flights were more than one hour late, a report by the Air Transport Users Council has revealed.
The Midlands-based group last week announced that it had gone back into the black notching up annual pretax profits of £2.1 million.
Only Air Atlanta Europe fared worse than bmi with just over 40 per cent of its services running more than an hour late.
Overall airline punctuality slumped over 2004's holiday season, with just over nine per cent of charter flights to and from major UK airports more than 60 minutes late, compared to 7.8 per cent in 2003.
The statistics, based on arrivals and departures information from the Civil Aviation Authority, also showed that the average delay in summer 2004 was also up nearly four minutes, from 19.7 minutes in 2003 to 23.4 minutes.
The best performing carrier over the summer was Iberworld of Spain with only 2.3 per cent of flights more than one hour late and average delays of 9.9 minutes.
The top UK airline - and second to Iberworld - was Britannia Airways. The airline had received criticism in last year's report for an increase in delays. However, it recovered with a 14.9 per cent drop in flights delayed over an hour to just 4.6 per cent. Average delays for the airline were 13 minutes.
Air Transport Users Council chairman Tina Tietjen was disappointed that the only major UK charter carrier to improve punctuality was Britannia.
She said: "We certainly hope this just a blip and urge the charter airlines to ensure all the hard work they have put into improving their punctuality since 2000 does not go to waste."