Santander UK insists tonight that the downgrade, which essentially means its credit is less trustworthy than previously, has "no impact" on its business.
It is not the first time that UK banks have had their soundness judged in this way. A few months ago several UK banks were downgraded.
Yet those changes were as a result of changes to the way the Government regards them. Barclays, RBS and others were judged as less trustworthy because the government plans to make them separate out their investment banks from normal high street banks so that none is "too big to fail".
That will essentially remove a Government guarantee, so a bank that got into trouble will not, in future, be bailed out by the taxpayers.
This is a different moment. Santander UK has been downgraded because of the troubles in the Eurozone. Even though it is run separately to its Spanish parent company, it is still judged to be more risky because of its associations with Spain, a country whose economy is in recession and whose banks are under attack.
To my mind, and Treasury sources appeared to admit the same, this is the first time a UK high street bank has taken such a knock because of the chaos across the Channel.
It is a reminder, if one were required, that we are not immune from what is going on.