From what I know, the 1.8T for a 2011 TT should be the EA888 engine, which is chain driven, not belt. I think the 2.0T TT's up till around 2010 were still using the older belt drive driven engines (golf mk5 gti engine). The easiest way to tell is pop the bonnet and look at the dipstick location, if it is at the front is the older belt driven engine, the 1.8 / 2.0 TSI's have dip stick on the left hand side of the engine. Google (google images) 2.0 tsi or 1.8 tsi engine, and then golf gti mk5 engine and you'll see what I mean.
Being a 2011 model it will likely have the earlier version of the tensioner, newest version came out circa 2012.
sure someone will correct me if i'm talking rubbish...