Hi, I would read some reviews from the likes of Autoexpress, Carbuyer, Whatcar etc, for a realistic mpg.
Carbuyer suggests – “Renault’s claim of 58.9mpg seems achievable; our test drive on faster roads returned over 53mpg, and staying at lower speeds would increase the fuel efficiency further still. That compares well to hybrid SUV rivals like the Kia Niro and the Toyota C-HR.”
https://www.carbuyer.co.uk/renault/arkana/mpg
However, the Arkana won’t be as engaging to drive as your current vehicle, if thats important.
As your your already on the scheme you should get the £750 new car payment, but may miss out on any good condition bonus terminating early.
If you ordered the Citreon and it was delivered when your current lease was up, you would get the £250 back. 🙂