This is obtaning monies by deception and is a dismissable offence, if you can demonstrate that he has really done these things.
Take him to one side and tell him he is required to attend a disciplinary meeting, as you reasonably believe that he has knowingly submitted incorrect timesheets. Confirm this in writing, giving him min 24 hrs notice. He can have another employee as a witness, so can you. Give yourself time to gather irrefutable evidence.
Ask him to explain himself and present your evidence. Take notes of EVERYTHING that is said.
If he has more than one years service, you must adequately demonstrate this has happened and you could dismiss him for gross misconduct. He has the right to appeal within 7 days. You cant hear the appeal, somebody equally or more senior must do it.
Less than one year, issue contractual notice. I cant think why you or his colleagues would want this work shy waster to stay on - he is a drain to your business in more ways than one!
Good luck