Irish accounting firm Deloitte has formally stepped down as auditors to Ulster Bank after 16 years in the role.

This emerges from a companies office filing by Ulster Bank, which shows that Deloitte resigned on April 5th.

EY has taken over the role with Ulster Bank in a change prompted by a tender process initiated in 2014 by its parent company, Royal Bank of Scotland, to appoint auditors across the group.

Deloitte was paid €1.1 million, excluding Vat, as auditors to Ulster Bank Ireland Ltd in 2015, up from €933,000 a year earlier.

Its audit fee fell by €12,000 to €906,000 last year but its pay for assurance services rose to €210,000 from €15,000 previously.

EY is also auditors to Ulster Bank's rival, KBC Bank Ireland, a position it has held since before the global financial sector's meltdown in 2008. The firm had been previously been auditors to both Anglo Irish Bank and EBS Building Society (now part of AIB) at the time of the economic crash.

Deloitte took over from KPMG as Ulster Bank's auditors for the 2000 financial year, remaining in the role after the crash, which resulted in a £15 billion bailout by RBS of its Irish subsidiary.

The firm is currently auditors to AIB, having taken over the role from KPMG for the 2013 financial year.

Rival PwC audits both Bank of Ireland, a role it has held since before the crash, and Permanent TSB, which it took on for the 2013 financial year.

KPMG is the only one of the so-called Big Four accounting firms that does not currently audit one of Ireland's main retail banks. At the time of the crash, it was auditors to AIB, Irish Life & Permanent, Irish Nationwide Building Society, and Postbank (a joint venture between An Post and BNP Paribas).