Flybe like the majority of European carriers file repetitive flight plans with the central flight planning unit in Brussels. These are plans held on services which operate at regular intervals with a high degree of commonality. These RPL's, as they are called, are filed just twice a year at the start of the summer and winter schedules and are used so that airline operations departments do not need to send out flight plans every day. Instead they just need to inform Brussels of any changes that might occur on a particular flight, such as an aircraft type change or time of departure. They are also expected to inform Brussels when the flight is not intending to operate as this will have an effect on flow management predictions, ATC and airport operations.
The cancellations referred to are simply Flybe complying with this requirement due to the bank holiday on Monday and will be mirrored by similar cancellations amongst other point to point carriers. Hub and spoke type operators and those who operate spoke services as part of an alliance will see fewer cancellations due to the difference in their business model.