At the start of tonights task one of the housemates was saying "did you hear the announcer say 'Tonight the housemates complete their final task - LIVE' ?".

How could they hear what was being broadcast live on channel 4?
I originally thought maybe there was a TV in the camera run but surely they would leave the sound turned up

yea i was wondering this, perhaps a background noise from the BB booth? Maybe someone was playing about with the editing and it echoed into the booth.

Well they where all sat on the bed and I was sure it was "This is Big Brother...." at the start of that.