Contractors day rates and hours worked!

[Marcellus]

I am just pondering how this is managed.

You have a contractor working for a company at an agreed £x per day.

Is there a "recognised/standard" number of hours per day for which the £x is charged?

and then what happens if that number of hours are exceeded?

[Marcellus]

Cheers guys, it wasnt for me but for a "friend" I'll pass on the sentiments of the comments.