Pete
These aircraft are being used because there were alot of tech aircraft around the network yesterday, 4 in EDI alone. They are also being used periodically to cover because Flybe expected the 175s to be delivered by now thus substituting these Q400s. The 175's are delayed by about a month. The first one is being delivered next week I believe to enter service the first week in August.
The South African Express deliveries were put back due to a problem with the South African Government & funding. This has apparently been resolved so the Q400s will be leaving soon. I am not privy to any dates though, sorry.