Part time hours contracts question

Any HR types here or general employment law type gurus?

What do you think of this situation? Im not sure if theres any set way of doing this but suppose it would at least help resolve an argument!

Permanent Part time contracts...

1 person says to stipulate the exact working hours of the part time employee in their contract so they can't play funny buggers with their hours.

Another person says to only stipulate the total working hours per week of said part time employee.

Who is right and who is wrong? Are both right depending on business needs?

Any views would be appreciated:-D

Don't know if here or The Holy Ground was through best place for this question!

Cheers!

I'm not in anyway, shape or form HR, but have had dealings with contracts and been involved at a "union" level.
As far as I'm aware, you can have the contract both ways. I've represented part timers that had a contract for 20hrs, and their T's & C's stipulated a roster would come out at an agreed timescale with their rostered hours on it. This gave the company flexibility with the staff and the staff knew weeks ahead what they were working.
I've also had part timers with hours stipulated on their contract, this removes the flexibility but then everyone knows where they stand.