I've gave up using BD for my NCP parking and now just credit the stay to my worldpoints card. The exchange rate is pretty dreadful (2 points per pound (I am on double points) 1 point = 1 pence) but at least the points post within a day which saves chasing them up.

I've probably spent about £400 @ NCP car parks in the last 3 months which would have been worth 4000 DC miles. The Worldpoints return is much worse but saves me the hassle of emailing to chase up these miles.