Watching some of the early DOND shows on Challenge I'm reminded of a time when the banker made much more generous offers for what was on the board. Can anyone remember when that started to change? Was it gradual or was it in response to more contestants taking less of a risk (perhaps because of the economic downturn) ?

I think the two big games it can be pinpointed to are Trevor's (March 2006) and Sarah's (May 2007), with the former marking the end of 2005/early 2006 ridiculously generous late game offers and the latter marking the abrupt end of Wakey Winter-esque offers (which were ridiculously generous at the start and generally slightly less generous though still good for the board towards the end).

Thanks, I'm assuming you're referring to Trevor who won 1p having still had the 250K at 5 box but was offered just 10K a very low offer even by today's standards given the 250K still in play.