Which is the most economical car to own fuel and tax wise

Daughter runs a 52 reg Renault Clio 1500dci, £30 a year road tax, good on fuel, reasonable priced spare parts, insurance reasonable. Its been that good she has had it from it being 1 year old.

If she has had it from being one year old, that would make her no more than 9 years old!

Does she drive it off road?

a lot depends on your mileage and the type of driving you'll be doing ... will you be mainly doing short city journeys, or motorway miles ?

Short journeys

A 1970 Lotus Elan is zero tax. It might use a drop more fuel than a few of the boring modern alternatives but has the advantage that it appreciates rather than depreciates.

Also you can earn on this car by parking outside peoples' homes when they want to impress visitors.I think Steve McQueen owned several for use in films.

a polo blue motion

Sounds like something you would see in the bottom of a toilet bowl.

The most economical car is electric, like the nissan leaf.

http://www.topgear.com/uk/car-news/nissan-leaf-driven-2010-07-26

Zero road tax.

Just plug it into the mains to charge up, fuel costs 10 time less than petrol. And if you happen to go to London, you don't need to pay the congestion charge.