I've been told I can get 60 mpg from a BMW 120d dont know what age it needs to be ?

Also the Citroen C3 can do 65 MPG

I do 3000 miles a month so need a car that can give me a good return on my petrol allowance to fund the purchase of it.

If i can get down to 8p a mile I'd be looking at covering the cost of the vehicle around 12K in a years allowance.

Any advice is appreciated.