The revelation of a £1.5 billion black hole in the London operation of Credit Suisse is acutely embarrassing for the bank. Only a week ago its directors were preening themselves over their supposed transparency and bragging about how little they had flushed away in toxic American sub-prime loans.

Only 48 hours ago the Qatari Government, having combed through dozens of Western banks in search of a paragon of transparency and financial virtue to invest in, plumped for Credit Suisse and aggressively piled into its shares.

So confident were the Qataris over the quality of the bank that they even started to write put options on its shares — in effect insuring counter-parties against a sharp fall in the share price. Cue Credit Suisse’s bombshell and a slide of as much as 9 per cent in the shares yesterday. It is teeth-clenchingly bad timing.

Credit Suisse owes its shareholders a much fuller explation than the thin statement yesterday and unsatisfactory briefing from Brady Dougan, chief executive. The phrase “mismarkings and pricing errors by a small number of traders” raises far more questions than it answers.

1. Why were traders pricing these positions in the first place? Surely, this was the function of valuers in the middle office on the other side of a hefty Chinese wall?

2. If traders – with an obvious conflict of interest – were valuing positions, why weren’t there independent safeguards?

3. Was the mispricing due to innocent cockup, overoptimistic assumptions in the pricing model or plain dishonesty and bonus greed?

4. How much of the £1.5 billion pain was due to the mispricing and how much due to deteriorating markets?

5. Why was the problem not picked up in the full-year results a week ago, when every position should have been double-checked? Its hard to imagine a more obviously sensitive area than “synthetic CDOs” – complex securities crying out for the most rigorous scrutiny.

6. What were the auditors KPMG doing and why was their review conducted only after the full-year results?

7. What safeguards are in place to prevent similar valuation failings in other parts of the bank?

Responsibility for shortcomings of this magnitude has to go higher up the bank hierarchy than the traders. Shareholders must have confidence that the bank takes this kind of incompetence seriously. A senior head must surely roll.

Just as investors were starting to hope that even the most delusional bank had woken up to the severity of the sub-prime slump comes this setback. With the Société Générale calamity illustrating the weaknesses in controls, investors could be forgiven for mistrusting every bank’s official numbers.

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