Additional hours clause in contract legality,Scotland

Hi all,

I have been given a contract from one of the big 4 and there is a section I am not clear about...

"You are expected to work the hours necessary to perform your role. You will be expected to work a reasonable number of hours in excess of your contractual working week commensurate with your professional responsibilities to satisfy client demands. No additional remuneration will be paid in respect of such overtime."

To me this seems to be saying they can ask me to work additional hours without being paid.

Is that what it's saying and if so is that legal?