I would steer clear of Citroen, unless its the C1. Several friends of ours have had bad experiences with them across the range: C3, C4, C and C8. The C1 is identical to the Peugeot 107, and the Toyota Aygo (they are built in the same frigging Slovakian factory) but they are all cars which are more like...shoes really.
If you wanted more size, you could go up to a Renault Laguna size (which is fracking huge by british standards).
or you could go a little cheaper (therefore smaller) to the likes of the Peugeot 207 SW
Every singe one of these come in 1.4/1.6 diesels that are over 60 mpg.