What the hell was David Cameron thinking?

The Prime Minister's intervention over Jimmy Carr and his tax affairs seems very short-sighted indeed. From a purely communications perspective my feeling is it could be damaging and do him and the Conservative Party more harm than good for the following reasons:

1. It was a tactical not strategic intervention
It seems clear to me that David Cameron and his team had thought through his intervention before it was made. Indeed the PM himself admitted as much in his interview with ITV. My assumption is the PM's team wanted him to intervene before a Lib Dem minister could seize the moral high ground. This is a danger of coalition politics but, by leaping in two footed, he has failed to think beyond the initial media coverage portraying Cameron as on the side of the majority of people.

2. He missed a great opportunity to tell a positive story
George Osborne announced in his Budget this spring substantial new measures on tax avoidance so David Cameron didn't need to get dragged into this row. Instead this was a great opportunity to state exactly what the government is doing already. Of course Cameron should look to demonstrate understanding of what families are currently going through but targeting an individual was not the way to do it. My proposed answer would have been:

"It isn't for me to comment on individuals but my government has made huge strides in this area already. In the Budget the Chancellor announced significant changes to the tax system to make it fairer and simpler which will benefit everyone. Ultimately we want to see a tax and benefit system which rewards those in society who work hard, take risks, create jobs and make a positive difference to the lives of others."   

3. It gives the media licence to go digging
This could well come back to haunt the PM. With the media, egged on by the opposition, keen to paint him as an out of touch toff it will only be a matter of time before a newspaper finds evidence that a) Conservative donors b) friends of the PM, or c) both have used these tax avoidance schemes. Then what will David Cameron say as he will have to say something having already passed judgement on Jimmy Carr?