Prime minister's questions sketch
By Nick Assinder
Political correspondent, BBC News website
Yesterday it was Alistair Darling who was facing allegations of incompetence - Gordon Brown knew today would be his turn.
Mr Cameron had the prime minister in his sights over missing data crisis
He attempted to take some of the heat from the looming storm by using the very first question of PMQs to offer his full apology for the missing data crisis.
His defence was simple - this was a case of proper procedures having been ignored and it should not have happened. Investigations had been launched and procedures tightened - in other words, the stable door is being locked.
It was clear from his robust performance, and from comments from Mr Darling earlier in the day, as he engaged in a "masochism strategy" tour of media studios, that this is to be the government's defence.
It was not ministers' fault and they should not be held responsible for the actions of any individual who deliberately flouted the rules.
It did not wash with the opposition and it remains to be seen whether it will wash with the electorate.
Both David Cameron and acting Liberal Democrat leader Vince Cable - having chopped away at Mr Darling - are now turning their fire firmly onto the prime minister himself in the hope this day will be seen as the Labour government's own Black Wednesday.
Mr Brown denied there was any systematic breakdown
They believe the government's reputation for competence has been damaged, perhaps fatally, and that voters - at least 25 million of them - can no longer have confidence in ministers' ability to protect them or their families.
The charge is, as declared by Mr Cameron, that this control freak prime minister is incapable of running the country.
Mr Brown, the Tories point out, ran the relevant departments for a decade and was personally responsible for merging the inland revenue and customs departments and cutting jobs.
It is no good, they claim, blaming individuals - there has been a systematic breakdown and citizens cannot trust the government to protect their most sensitive data.
"Does he feel at all responsible for this?" asked Mr Cameron.
The answer, unspoken perhaps, was none the less a resounding "no".
That brought the most stinging rebuke from the opposition leader.
"People want him to stand up, show some broad shoulders, be the big man and take some responsibility," he said.
What he meant was, the prime minister has attempted to rebuild his dented credibility in the wake of the disastrous non-election and a series of other setbacks by playing the broad shouldered, big man, and this crisis had blown the tactic out of the water.
Lack of blood
Meanwhile, the least the government should do is re-think the controversial ID card proposals.
Voters would find it "bizarre and weird" that the prime minister was determined to press ahead regardless, said Mr Cameron.
Mr Brown may have looked uncomfortable and his own side appeared to be in shock - but Mr Cameron failed to land any lethal blow.
He is, perhaps, playing a longer game on this one, believing that the worst is yet to come.
Nonetheless, the Tory benches looked like they had been expecting more and many appeared disappointed by the lack of blood. But this is far from over.
Mr Brown may have escaped this question time mauling in one piece but there is still no way of knowing how this crisis is going to play out.
Further revelations, any suggestion that criminal activity is involved, and things will take another very nasty turn for the government.
In any case, there remains the fear on the Labour benches that Mr Brown will struggle to regain his reputation for competence in the wake of this affair.