http://www.fuel-economy.co.uk/calc.shtml
372 miles @ 40 mpg @ 99p Litre = £41.86
372 miles @ 35 mpg @ 99p Litre = £47.84
That's a saving of £5.98 per day x avg working days in a year 220 = £1,315.60 assuming you travel that far every day at 40mpg.
Now, you could get a small engined diesel cars (one of those 70mpg ones):
372 miles @ 70 mpg @ 109p litre = £25.36
Thats a saving of £22.84 a day vs your 35 mpg x 220 working days = £4,945.60 per year
When I started working this out, I was going to point out that its far more fun in your car than it would be in a diesel. However looking at the cost saving, if you travel that far every day might be better off changing your car! lol