Fiesta 1.25 Zetec with poor fuel consumption and petrol smell in cabin at speed.

Hi All,

I wonder if anyone out can help me with a curious problem affecting a
friend's Ford Fiesta? (T-Reg, 1.25 Zetec engine on 78000 Miles)

The car is using more petrol than usual and there is a smell of fuel
in the cabin when the blower fan is switched on, but these problems
only appear when the car is driven on a long journey over 60mph.

The car seems to run fine otherwise when doing its usual short trips.
I've had a good look around under the bonnet and underneath and I
can't see any obvious signs of leakage or perished pipes.

The air filter looks fine, the plugs were replaced recently and there
is no engine management light up. I'm not sure where to look now! Does
anyone have any suggestions?