The Director of Corporate Enforcement Paul Appleby has said that the “investigative phase” of his office’s investigation into Anglo Irish Bank is “almost complete” and that he expects to be able to sign off on a number of important remaining matters over the coming weeks.

Five "extensive" investigation files were sent by the Office of the Director of Corporate Enforcement (ODCE) to the Director of Public Prosecutions last year and a further three large investigation files were sent in the first three months of this year, Mr Appleby said at the launch of the office's annual report for 2011.

"It is of course entirely a matter for the DPP to determine if, and to what extent, any of the extensive investigation files which she has received from this Office and the Garda Bureau of Fraud Investigation warrant prosecution," he said.

"ODCE staff remain available to address queries from the DPP's office in order to assist with its deliberations on the investigation files. Every consideration will also be given to fulfilling any future DPP requests which may be made for additional evidential materials."

Minister for Justice Alan Shatter said the Garda Commissioner had confirmed the Garda investigation is "substantially complete" and that gardaí are working closely with the DPP in relation to the investigation files.

"I have said before that I share the sense of frustration at the length of time which investigations of this kind can take but what is important now is that nothing be said which would in any way risk the possibility of prejudicing any criminal proceedings which might arise," he said.

The office's investigation into Anglo has examined five areas – loans by Anglo to purchase its shares, in July 2008 in particular; the refinancing of directors' loans over the end of Anglo's financial year for several years; a loan to an Anglo director close to the end of Anglo's year-end in September 2008; the suspected failure by Anglo to keep a proper register of loans made to its directors and connected persons over a number of years; and the content of Anglo's public pronouncements about its financial position, particularly during 2008.

The Garda Bureau of Fraud Investigation is carrying out a separate investigation into the back-to-back financial support between Anglo and Irish Life and Permanent over Anglo's financial year-end in September 2008 and the bank's loans to the so-called Maple 10 customers to buy a stake in the bank held by businessman Sean Quinn.

"There is no area where we have not sent a file to the DPP," said Mr Appleby. "There is only one area which I would characterise that we have sent an initial investigation file – that is in relation to the adequacy of Anglo's financial and other statements in 2008."

The office had decided to carry out no further work on this strand of the investigation pending contact with the DPP's office, which if it feels further work is required, his office will consider that, he said.

A "very substantial amount of material has gone to the DPP's office at this stage" – about 150 lever-arch folders of documents have been sent to the DPP by both the ODCE and the Garda Bureau of Fraud Investigation, he said.

The DPP has been "very much engaged in evaluating that material" and they are taking legal advice on the investigative files, Mr Appleby said in response to a question about whether the DPP had sufficient evidence to mount a prosecution.

About a third of the ODCE's staff, roughly 16 officials, are working on the Anglo investigation, which is more than three years old. Mr Appleby said he was aware of the public frustration about the length of time that the investigation has taken but that it has been faced with challenges.

"We have had our difficulties and frustrations as well in moving this forward. People just need to know that there was a huge amount of material which had to be evaluated. A large number of witnesses had to be interviewed. You will aware from other instances that cooperation was not always forthcoming," he said.

"The length of time this has taken is simply a factor of the requirement to undertake the investigation to appropriate legal standards. If there is a prosecution in due course, there are going to be severe challenges presumably; the standards of investigation have to be able to address and meet those challenges."

The ODCE is now getting "substantial cooperation" from more than 10 witnesses whom Mr Appleby had previously described as reluctant. "Statements have been obtained from the vast majority or close to finalisation in one or two cases," he said.

Mr Appleby said that the investigation could have moved faster with more staff but having a greater number of staff would not have greatly reduced the length of time taken to carry out the investigation.

"If we had double the staff on this investigation, it wouldn't have been done in half the time. There would still be the same sort of issues that have cropped that have caused delayed. If we had had double the staff, we might have shaved a couple of months off the investigation but that is as much as we would have done," he said.

Mr Appleby said that he did not think that there would be a requirement for "expert jurors" to hear any prosecution cases arising from the investigations into Anglo, though he said that it would be "a difficult series of cases" if the DPP takes a prosecution over one or more strands of the investigation.

Speaking at his final annual report presentation after 10 years as Director of Corporate Enforcement, Mr Appleby said that he would retire at the end of August after agreeing with the Government in February to remain on in an acting capacity for six months. An individual had been identified to succeed him after a competition to find his replacement, he said.

Mr Appleby gave the Government a month's notice of his indication to retire at the end of February as per the terms of his contract. He said that the notice period for the retirement or resignation of his successor "should be put in at a minimum of six months".

He had told the Minister for Enterprise Richard Bruton in January that it was a good time for him to leave as the Anglo investigation was "sufficiently advanced" and that he was "clearly happy" that there would be no damage to the investigation as a result of his retirement.

Mr Bruton welcomed the announcement from Mr Appleby that nine files had been sent to the DPP's office arising from his investigation into Anglo and that the investigation was almost complete.

"The matter is now in the hands of the DPP who is legally independent and it is for her to decide what, if any action, she considers appropriate," he said.