Thank you everyone, that's gave me a few starting points.
That's really helpful, thank you. We initially looked at the Skoda Octavia, we do want a fairly big boot as she often goes to Doncaster to see her family with about 2 massive suitcases and other bags. Usually a nightmare when changing trains at Darlington/York.
We did look at the Skoda Octavia first as taxi drivers usually use the we know there's a lot of room and we assumed they'd be good on fuel. But someone did say they were probably too big and suggested a Skoda Fabia. We'll have a look at the Nissan and Honda. If we can get a reliable and safe one for £5000 then that is a lot better than either of us expected.