If you want a saloon, I think I would go for a BMW320 diesel - around 49/50 mpg and from our fleet experience very reliable. Estate - probably again a BMW320 diesel.
However, 'thinking outside the box', I would seriously consider a Seat Exeo CR TDi, 50 plus mpg and it is virtually the same as an Audi A4 but you could get a better spec for your money than you would for a BMW or Audi. Reliabilitywise, I understand they are extremely reliable (VW engineering)
V50 gets 60+mpg on a l o n g run, currently averaging 50-55mpg. I fancy the "Stop/start engine"... switches off when you stop in a cue and disengage gear... on again when foot goes on clutch.
If you can stand the name, Skoda Superb.
2 litre TDI gives 140bhp, 6 speed gearbox, all the usual bells and whistles and gives >50 mpg even at high speeds. Also VW reliability at reduced cost. Check one out. You won't be disappointed.
Surely we've got beyond "the Skoda name", by now. I have to agree that the Superb would be my choice if I wanted a very roomy, very well appointed, very reliable and superbly fuel-efficient car. The diesel actually does 45-64 mpg, amazing for such a sizeable vehicle. It gets an owner satisfaction score of 94% in The latest Which? Car Survey.
2 problems with Superb- firstly it's the only car i know that is bought brand new ...by mini cabs drivers
Also -i think it looks very clumsy and awkward (estate is okay) -and i'm someone who is 99% neutral on car styling
If, however in the unkikely scenario that you are reguarly travelling five 6ft plus people -then Superb is one to go for