This pointed reminder of the fragility of the Shia-led government follows previous bombings in August and October which killed or injured more than 1000 people. It is a change of tactics by the Sunni insurgency which targeted mosques and markets where Shias congregated, and an indication of a new momentum from al Qaeda with the aim of eroding confidence in the election, which depends on safe streets and a return to normal life.

Against the background of the Iraq inquiry under Sir John Chilcot, it is a bleak reminder of our failure in that country. The central question so many people want answered on whether the invasion was legal may never be answered, but the evidence of senior civil servants, military chiefs and diplomats so far has revealed that fears about legality led to secrecy which hampered military preparations and planning for a post-war strategy.

The appearance of Sir John Scarlett, chairman of the Joint Intelligence Committee (JIC) – the senior UK intelligence body – held out the prospect of a definitive statement on the most controversial aspect of Britain’s engagement in the war: the claim that Saddam had weapons that could be deployed within 45 minutes. Doubts over the

accuracy of the dossier in which this claim was formulated led to serious distrust of Tony Blair by the British public.

Sir John, the man who drew up the dossier, distanced himself from the foreword written by Mr Blair, but provided no new information in confirming that Iraq had disassembled missiles that could hit Israel and had no warheads that could carry chemical or biological weapons, but that it was assumed to be deliberate concealment and therefore not “game-changing”. His get-out was the stock one that with the benefit of hindsight, things might have been done better,

That Sir John Scarlett could tell us more can be deduced from the chairman’s statement that other intelligence matters relating to Sir John’s time as head of MI6 would be dealt with behind closed doors. It is only the

second week of this inquiry, but all the signs point to an expensive whitewash.

The urgent need is for stability in Iraq. This new atrocity again raises doubts about the readiness of the Iraqi security forces to take over when US combat troops withdraw, especially when attacks on government targets suggest complicity.

Iraq must find a way to build bridges between its different groups, and desperately needed physical reconstruction will be vital in that process. It is due to auction the rights to some of the world’s largest and most promising oil fields to major international oil companies later this week. The bombing should not postpone that and further damage the slow return to stability.