"There was a period of remorse and apology for banks, and I think that period needs to be over," Barclays' boss Bob Diamond declared last year. Not if Wednesday's news is anything to go by, Mr Diamond, not by a long way. The bank yesterday agreed to pay fines totalling £290m to British and American authorities, to settle charges of market rigging. The £60m it will hand over to the Financial Services Authority alone is the biggest penalty ever levied by the City watchdog – yet the nature of the alleged transgression is so fundamental, so serious and, according to officials, so "widespread" that it appears utterly inadequate. Nor will the decision of Mr Diamond and his team to apologise and forfeit this year's bonuses take the sting out of the matter.

What regulators appears to have uncovered is a scam at the heart of a £350tn market; one that ultimately affects how much families pay on their tracker mortgages, as well as the costs of transactions for big City institutions. It should not be settled with a fine, no matter how large, but must be followed up with a further investigation into Barclays – making public just how many employees took part (rather than yesterday's mentions of Trader C and Manager E), and how they will be punished, up to and including criminal proceedings. Not only that, but it also needs to be uncovered just how far this market-fixing went. Certainly, the clear implication of yesterday's comment from the Commodity Futures Trading Commission that Barclays' staff "co-ordinated with and aided and abetted traders at other banks" indicates that Mr Diamond will not be the last chief executive in the firing line over this issue.

Strip away the acronyms and the charges against Barclays are straightforward. Its traders and senior management are accused of tampering with two key interest rates to bolster their own profits. And they apparently did this not once, but repeatedly over four years. Indeed, the practice seems to have become so widespread that staff joke about it in emails: "Always happy to help, leave it with me, Sir."; "Done … for you big boy"; "I love you". This from the bank that earlier this year held citizenship days for its staff – and which, through state guarantees and emergency provisions of liquidity, has been supported by the British taxpayer.

There has been much talk about banks being too big to fail, or too big to bail. The picture presented by Wednesday's charge sheets is altogether simpler: throughout boom and bust, Barclays staff saw themselves as being too big to play by the rules. And the likely result is that everyone else paid millions more than necessary to borrow. What's more, they do not look like the only ones: this has all the makings of systemic scandal.