Didn't it run to time one year recently to everyone's surprise?
Happened a couple of times. The famous one was in 1992 when they ran short so Paul Merton, who had just won the final viewer-voted award, was invited to immediately come back up on stage to do another acceptance speech (ie, do some of his stand-up) to fill time. It was supposed to be followed by a Beadle's About repeat and Merton said "The longer I talk, the later Jeremy Beadle comes on".
In 1998 it was scheduled in a two and a half hour slot, the longest it had ever been, and finished with about twenty minutes to go, so we had a couple of trailers and then they announced "Now we return to the British Comedy Awards", but they didn't really, they just showed some of the nomination clip packages again.