My last fill up when the light came on and DTE was zero (well it dissapeared about 20 miles from empty to ****), was £93. If I pushed it too far past zero DTE, I wouldnt be able to use pay at pump at Tesco as it has a limit of £99!   
haha now you mention it thats what i was doing!  it was getting high and i was wondering what the pump would do and if i'd get in trouble as it was a night and theres no other way to pay  just went on forever. 
  
on a similar note, i have run the zed out of fuel before.  probably worth its own topic about what to expect