Well there's your answer, or at least part of it...

MacHeath left a comment here as follows:

Which brings me neatly to another point - do we know how much is being paid out in compensation for these [NHS] mistakes, to say nothing of the expensive long-term care needed when cancer has gone untreated for years?

From the BBC today:

The rising cost of litigation means the NHS has had to put aside a record £787m this year to cover the cost of claims.

Let's round that up to £1 billion to cover all the internal reports and enquiries and so on, which makes about one per cent of the NHS annual budget. Obviously, I don't know what the comparable figure for private hospitals is, or how much it would cost to insure against the risks.