In the EC lorry drivers (for non-exempt road vehicles over 3.5 tonnes) are only allowed up to 4.5 hours continuous driving time without a break, up to 9 hrs in one day. This is presumably to prevent fatigue causing accidents. British domestic law I think allows up to 10 hours driving where the EC law doesn't cover, with a total of 11 hours "on duty",
And arent we advised not to drive for more than 2 hr without a break and thats in your avrage 90 bhp saloon car