Jamie Dimon is right to suggest that treating agency MBS as inferior to covered bonds is unfair, but the popular reaction to his comments is wrong. As senior economists at the BIS highlighted this week, the last thing banks need to be doing is holding more sovereign risk – and does the US really want government support for mortgages even more tightly woven into its financial system?

JPMorgan Chase & Co chief executive officer Jamie Dimon chose to wrap himself in the flag in an interview with the Financial Times published last week, calling the Basel III framework “blatantly anti-American”.

“I’m very close to thinking the US shouldn’t be in Basel anymore,” he was quoted as saying.

An example of the Basel Committee’s anti-Americanism? The way in which covered bonds have been deemed sufficiently liquid to qualify for LCRs whereas “government-backed mortgage-backed securities in the US” (the FT’s words; there is not a direct quote on the asset class from Dimon) are less favourably treated.

Many commentators, particularly in the US, agreed with Dimon that agency MBS should be considered at least as liquid as covered bonds.

Without pretending to be experts on the US markets, we have heard no reason to disagree with this.

But to go on to argue – as some excitable critics have done – that covered bonds do not deserve such privileges is wrong.

CNBC’s John Carney, for example, said: “They are the only privately labelled structured security [that] can be used to meet the liquidity buffer requirements. Otherwise, only cash or government securities can be used to meet these requirements.”

This is simply wrong. Non-financial corporate bonds, too, are deemed eligible for liquidity buffers. But unlike covered bonds, almost all are too lowly rated to qualify. Covered bonds have had to work hard to achieve their potential status.

Carney then argues – as did others even before Dimon’s comments – that creating what then becomes a uniquely privileged status for covered bonds would increase risks to the financial system by unduly supporting the asset class.

If this is true then surely the answer is not to narrow the range of assets eligible for liquidity buffers further still? For excluding covered bonds would leave government bonds as the only game in town.

In the latest Bank of International Settlements quarterly review, published on Monday, senior economists Michael Davies and Tim Ng highlight the rise of sovereign credit risk and the dangers this gives rise to.

“Bank supervisors may need to closely monitor the interaction of sovereign risk with regulatory policies that encourage banks to hold large quantities of public debt,” they suggest.

The European Banking Authority would do well to heed this call when drawing up the criteria that will decide what qualifies for different parts of liquidity buffers under CRD IV – and that also means considering whether any European mortgage backed securities should be eligible.

Meanwhile, if Dimon and others want to further enmesh government support for the mortgage market in the US financial system, they have every right to lobby for that. One might have hoped that JP Morgan’s takeover of Washington Mutual’s covered bond programme would have steered Dimon towards a market-led solution to his country’s mortgage finance problems, but covered bond issuance would become even less likely were the bid for agency MBS to be further boosted by their inclusion in liquidity buffers.

Then again, maybe that’s the American way.