Aircraft are not allowed to fly unless their systems are checked and rechecked by independent bodies in case they crash. The current Boeing incidents show what a big deal this is for the company when it all goes wrong.
The same could happen for banks because they are pushing the frontiers of technology.
But if one of them should crash, which is possible given fast growth and the commercial stress of a wafer-thin profit margin model, the taxpayer might ultimately have to bail out the customers to the tune of up to £85,000 each.
If there are millions of them that could be a lot of money.
What chance then that the regulator would have to appear before a Parliamentary Select Committee to explain how the bank was allowed to run such systems unchecked.
Surely it would be better to have a bank technology supervisor or some such to make sure these systems are robust so they don’t fall over?
It is also interesting that Monzo has well over three million customers and says it plans to double its user base by the end of next year to six million.
But the established banks are not shedding anything like as many customers as these figures suggest, so where are these coming from?
Quoting from a December 2018 FCA report, O’Shea points out a tiny fraction, only around 2.5%, of UK bank customers actually switch bank accounts every year.
And 90% of those switches are simply a reshuffling of accounts between the top four traditional banks.
The implication is that the vast majority of new challenger customer accounts are actually secondary accounts.
This matters a great deal because the higher-margin business is in that primary account activity, so challengers are being forced to survive at the very thinnest edge of the profit wedge.
Banks have to lend money to have a chance of being profitable, but these loans require a lot of regulatory capital to make sure the bank can cover any possible losses.
The established banks know this; but the challengers seem not to. Metro got its capital allocations wrong and the shares have crashed in spite of raising a £350 million loan to shore up its balance sheet.
The other banks also have to put aside substantial capital for their loans, and the chances are they will need to borrow.
The City is awash with money and pouring it into loss-making ventures seems like a good idea at the moment. Until the mood changes and then they run for cover.
That is when the music stops, as it inevitably will at some point, and that is also when the challenger bank model will itself be challenged.