The plane was due to leave Oman on Wednesday but remained grounded due to problems getting passengers on board.
The Cypriot government has criticised how the UK has handled information sharing after drone attacks.
The home secretary says the "incentives" will deliver a "significant saving to the taxpayer".
Baroness Heather Hallett said completing the hearings in under four years was an achievement but critics have questioned its cost.
The firm was unable to cope during high demand, Ofwat says, leading to "immense stress" for customers.