The fact that you are a temp is immaterial. If you work more than six hours in one shift, then you are entitled to a 20 minute break every 4 hours. It is generally up to the company when they would like you to take these breaks. To explain by example, I work 12 hour shifts, which means I am entitled to a total of 60 minutes break (3 x 20 minutes). My company asked me to sign a contract (which I was happy to do) that stated I would take 30 minutes during the first 6 hours of my shift, and the remaining 30 minutes in the second half of the shift, though neither break would be taken during either the first 2 hours or the last 2 hours. Now, that is what I agreed to by contract. Your place of work might want to ask you to agree to when you take your own allocated breaks.
Since you work a 10 hour shift, you are entitled under the law to a minimum of 2 x 20 minutes breaks. (And the odd shifty 10 minutes in the bog reading the paper!)