Form 20-F/A

(Mark One)



| ̈ | REGISTRATION STATEMENT PURSUANT TO SECTION 12(b) OR (g) OF THE SECURITIES EXCHANGE ACT OF 1934
|- | ----------------------------------------------------------------------------------------------

OR



|x | ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
|- | ------------------------------------------------------------------------------------

For the year ended December 31, 2011

OR



| ̈ | TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
|- | ----------------------------------------------------------------------------------------

Commission file number 1-10284





Allied Irish Banks,

public limited company

(Exact name of registrant as specified in its charter)





Ireland

(Jurisdiction of incorporation or organization)

Bankcentre, Ballsbridge, Dublin 4, Ireland

(Address of principal
executive offices)

David OCallaghan, Company Secretary

Allied Irish Banks, p.l.c.

Bankcentre, Ballsbridge

Dublin 4, Ireland

Telephone no: +353 1 6600311

(Name, telephone number and address of Company contact person)



Securities registered or to be registered pursuant to Section 12(b) of the Act

None

Securities registered or to be registered pursuant to Section 12(g) of the Act.

None

Securities for which there is a reporting obligation pursuant to Section 15(d) of the Act.

None

Indicate the
number of outstanding shares of each of the issuers classes of capital or common stock as of the close of the period covered by the annual report.



|                                 |  |                
|-------------------------------- |  | ---------------
|Ordinary shares of EUR 0.01 each |  | 513,528,806,391

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities
Act.  YesxNo ̈

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or
for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90
days.  YesxNo ̈

Indicate by check mark whether the registrant is a large accelerated filer, an acceleratted filer, or a non-accelerated filer. See definition of accelerated filer and large accelerated
filer in Rule 12b-2 of the Exchange Act.

Large accelerated
filerxAccelerated
filer ̈Non-accelerated
filer ̈

Indicate by check mark which basis of accounting the
registrant has used to prepare the financial statements included in this filing:

US GAAP ̈IFRSxOther ̈

If Other has been checked in response to the previous question, indicate by check mark which financial statement item the registrant has elected to follow.  Item 17 ̈Item 18 ̈

If this is an annual report, indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange
Act).  Yes ̈Nox



---

EXPLANATORY NOTE

Allied Irish Banks, p.l.c. is filing this amendment on Form 20-F/A to its Annual Report on Form 20-F for the fiscal year ended December 31, 2011, which was originally filed with the Securities and
Exchange Commission on April 24, 2012, to file certain additional Exhibits required by Item 19.

This Form 20-F/A consists of a
cover page, this explanatory note, the Exhibit Index, the signature page and the Exhibits. Other than as expressly set forth above, this Form 20-F/A does not, and does not purport to, amend, update or restate the information in any other Item of the
Form 20-F or reflect any events that have occurred after the Form 20-F was filed.



---

EXHIBIT INDEX



|               |  |                                                                                                                                                                                  
|-------------- |  | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|Exhibit Number |  | Description of Exhibit                                                                                                                                                           
|               | 
|1.1            |  | Memorandum & Articles of Association (incorporated by reference to Exhibit 1.1 of Allied Irish Banks Form 20-F for the year ended December 31, 2011, filed April 24,
2012).     
|               | 
|4.14           |  | Acquisition Agreement dated 26 May 2011 among Allied Irish Banks p.l.c., the Minister for Finance of Ireland and the National Treasury Management Agency and EBS Building
Society
|               | 
|4.15           |  | Note Purchase Agreement dated 26 July 2011 among Allied Irish Banks p.l.c. and the Minister for Finance of Ireland                                                               
|               | 
|8.1            |  | Subsidiaries List (incorporated by reference to Exhibit 8.1 of Allied Irish Banks Form 20-F for the year ended December 31, 2011, filed April 24, 2012).                        
|               | 
|12.1           |  | Certification of Chief Executive Officer pursuant to Section 302 to the Sarbanes-Oxley Act of 2002                                                                               
|               | 
|12.2           |  | Certification of Acting Chief Financial Officer pursuant to Section 302 to the Sarbanes-Oxley Act of 2002                                                                        



---

SIGNATURES

The registrant hereby certifies that it meets all of the requirements for filing on Form 20-F and that it has duly caused and authorized the undersigned to sign this Amendment to its annual report on
its behalf.

Date: 27 February 2013



|           |  |                               
|---------- |  | ------------------------------
|Signature: |  | /s/ Paul Stanley              
|Name:      |  | Paul Stanley                  
|Title:     |  | Acting Chief Financial Officer