I go up and down the country all the time
My experience over the last 3 years - figures from Full tank - Empty ish
Long run with Air conditioning turned off (saves quite a bit) - 360 - 380 miles
Some motorway, some A road, bit of town (air con onoff/) - 280 - 300 miles
all town and short runs - 260 miles
you can get at least 50 miles from the empty light coming on, if you turn the air con off!!
but its all worth it because after 2 hours getting to a customer, I'm fresh and ready to work. When I drove a Golf, I was ready to have a kip and go home again
;)
Mark