There was much tut-tutting on Monday when Sainsbury's shares crashed after the putative bidders from Qatar walked away.

They fell 115p to 440p - back below where they were before the Qataris came on the scene.

Surely the market had over-reacted. But on Tuesday the shares recovered just 5p of the lost ground. Then yesterday they were on the way down again, to the tune of another 19p, closing at 426p.

Still, that should not be a surprise. Even if the redoubtable Robert Tchenguiz - who also lost out with Mitchells & Butlers - stays put with his ten per cent as he says he will, others who followed him into Sainsbury for the ride are sure to cut their losses.

Even so, it is worth recalling that Sainsbury shares stood at 400p a year ago and that even now they are still 30 per cent dearer than their mightier rival Tesco on a price/earnings basis.

The wonder is not that the absence of the bid should destroy a quarter of the market value, but that the Qataris ever thought their indicative price of 603p was worth paying.

It was supposedly because Sainsbury has done the unfashionable thing and held on to its property freeholds.

Presumably, they are what attracted Mr Tchenguiz. They may interest him still.

One City estimate values the freeholds at 491p a share. But then commercial property was losing its gloss long before the credit crunch.

The era of dirt-cheap money available in limitless quantities that brought the world's biggest corporations theoretically within range of any bidder with the nerve to borrow the necessary billions is history. All very boring.

Well, up to a point.

We have still got Standard Life and Pearl scrapping for Resolution.

And the Carlsberg and Heineken project to carve up Scottish and Newcastle is already as ill-tempered as these things get.

Even without the borrowed megabucks it never quite stops.

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Now why do our big banks sit back and watch their share prices crumble away for all the world as if they were as deep into the sub-prime hole as their American counterparts?

If they are not nursing stupendous losses, surely all they have to do is say so, come clean with the numbers with enough bravado to convince everybody that they are the real ones.

Even if they are stupendous, the truth should be less painful than the suspicion.

The trick is the same - persuade the world that it is the whole truth.

The Royal Bank of Scotland fell another 17.75p yesterday to 438p, now yielding more than seven per cent for all the world as if a dividend cut was creeping on to the agenda.

Barclays is not far behind.

Yet one estimate yesterday was that Barclays - which has turned twice to the Bank of England for short-term help - could be looking at a £1.6 billion write-off and the Royal Bank at £500 million, albeit with the added uncertainty about what it may be finding at ABN Amro.

That would not be money to sneeze at. Just the same, it would leave these banks with 2007 profits of £3 billion or more.

Worse things have happened.