Fitch has affirmed RBS and Ulster Bank credit rating at 'A'.
The ratings agency has however downgraded Ulster Bank's outlook from stable to negative, to take Ireland's negative outlook into account.
It further says that Ulster Bank's ratings are sensitive to any change in Ireland's sovereign rating.
The ratings agency makes no reference to the recent difficulties in its assessment of Royal Bank of Scotland, Nat West or Ulster Bank.
Ulster Bank said this week that the cost of the technical difficulties will run into the tens of millions.
Fitch says the systemic importance of the bank, in the UK, means that it is likely the UK government will support the bank if the need arises.
In reference to Ulster Bank the ratings agency says that it retains its 'A' rating given that the parent bank will support the bank if necessary.
It says Royal Bank of Scotland has injected substantial capital into Ulster Bank and provides a third of its funding requirements.
