No it's 3 or 4 Allen bolts and it pops of infact Alfa replace this as a service item rather than removing the tensioner and idler separately. Take a look at my Gtv project (link below) there are a few pictures of the cam belt area.
Thank for your help Biffa
Had to take the whole plate off and loose alternator bolts aswell to get to broken tensioner bolt. Loosing the alternator bolts is the most difficult part - have to get under the car and there is lack of space to put hands in to hold the nut. And this part of the job requires 2 people. It took me many ours to do this job but I was lucky that tensioner bolt broke while changing the belt (not on the road) The nut was overtighten and the bolt had a crack