Airlines and operators were attempting to return their schedules to normal after thousands of passengers were stranded abroad over the weekend due to a wildcat strike by Spanish air traffic controllers.
Workers returned to work on Saturday night after being threatened with jail, but it could take until later today before flights are back to normal.
Dozens of services to and from UK airports were grounded as Spanish air space was closed, with Ryanair, EasyJet and Iberia cancelling flights.
The walk-outs, which began on Friday evening, left hundreds of thousands of travellers stranded.
Many people were forced to sleep at airports across Spain on Friday night and Saturday, with police providing blankets to keep them warm.
Dozens of flights from UK airports to Spain were cancelled and passengers were urged to contact their airlines before setting out.
Rescue flights were laid on by airlines yesterday to bring passengers home.