AIB shares could come under pressure next week as the bank drops out of the FTSE Eurotop 100 index on Friday.

Meanwhile the ongoing investigations into overcharging at AIB and revelations that some of its most senior former executives had used offshore investments that breached tax laws, are also beginning to weigh on its shares.

NCB Stockbrokers said yesterday that, while the financial impact of these revelations appear to be modest, the uncertainty surrounding the investigations will remain a "short-term negative" force for the bank.

AIB shares closed seven cents weaker in Dublin yesterday at €12.25. The bank would not comment on its forthcoming exit from the Eurotop 100 index.

The Republic's biggest bank won entry to the index a year ago and the shares had attracted wider investor interest as part of that index.

AIB is one of five companies, including the British bank Abbey National, to slip from the index. The changes are effective from the close of business on June 18th.

Inclusion in the Eurotop 100 index had helped to bolster AIB's share price in the months before its entry last year and provided technical support for the shares.

It entered the index at number 93. Membership of the index put AIB on the buying list of fund managers running investments that track the index's progress.

AIB had been a member of the Dow Jones Eurostoxx 50 index of leading euro-zone companies in 1999 but suffered a sharp fall ahead of a decision to relegate it from the index in June 1999. In 2002, it slipped almost 10 per cent after it became apparent it would not gain re-entry that year.

Yesterday the bank said that the internal investigation, headed by former comptroller and auditor general Mr Laurie McDonnell, would be delayed for a further six weeks and that the first report would be available at the end of July. The delay is due partly to the widening of the inquiry to examine all bank charges across a range of services since 1996. AIB has said that three reports will be issued in quick succession and that they will be given to the bank's board of directors and to the Irish Financial Services Regulatory Authority.

IFSRA has established that the bank overcharged some customers to the tune of €20 million and said it must pay them another €5 million in compensation.