But the travel operator said its first- half loss narrowed despite the setback.
Thomas Cook reported a pre-tax loss for the half year to 31 March of £252.2m compared with £309m the year before.
Northern European airspace was shut down for six days last month after Iceland’s Eyjafjallajökull volcano erupted, spewing ash into the air.
Thomas Cook said that – excluding the estimated impact of the volcanic ash cloud – it was confident of meeting expectations for the full-year.
Its shares have dropped by ten per cent since the disruption began.
However, chief executive Manny Fontenla-Novoa said the holiday market had bounced back following the initial disruption, with bookings in the United Kingdom up five per cent year-on-year.
He added: “Encouragingly, the market is getting stronger and stronger. At the moment, we’re out-selling our capacity. Our rate of intake is greater than the amount of bookings we’ve got left to sell.”