I find the bit about funding it through borrowing a bit strange.
Why does he need to borrow the money?
All he's doing is refunding money which he shouldn't have taken anyway.
And if 80% of people are fully compensated, and the remaining 20% are only half compensated, doesn't that mean the he's still 10% up on the deal?
It looks more like a cynical and desperate attempt to win back a few votes prior to a highly public by-election, than a mere U-turn.
And by now people will presumably have started receiving notifications of the removal of their 10% status; now HMRC is going to have to issue new tax codes to everybody in the country.
The hidden cost of administering this is going to be huge!
Supplement from 05/13/2008 10:18pm:
I'd say it's more of an escape route than a U-turn.