This short position paper by John Brewer is really worth a read for anyone interested in these issues:
Several years ago I described the impact debate as a sheep in wolves clothing – meaning that I never thought it was going to be the problem it appeared on the surface. This was an unpopular view. Developments in implementing the impact agenda, particularly by HEFCE, have seen my view vindicated. But the unfortunate association of impact in recent times with cuts in higher education, leaves no intellectual space for positive engagement with the impact agenda.