This would need sign off by line manager, head of dept, senior finance manager and 2 x cheque/EFT signatories. This kind of abuse is not happening on a wide scale, if at all.
Regarding my previous post (and not lightswitch's one)
I would hazard a guess that the line manager is a serious problem. If they know that the person is doing the journey, then the trip is signed off. The Head of dept more than likely trusts his direct reports and relies on them to keep expenses in line. The rest of the sign-offs just get the signed approval and pass no remarks.