A blowout in compliance costs is set to erode National Australia Bank's full year profit, with the bank still unable to quantify the financial impact of regulatory investigations into misconduct and legal breaches.Chief executive Andrew Thorburn yesterday signalled that the company would take "additional provisions" before the end of September to cover prospective fines, compensation and other remediation costs flowing from regulatory probes into the bank's activities.Evidence presented to recent hearings of the Hayne royal commission indicates that the additional provisions could reduce the 2018 annual profit by at least several hundred million dollars, but the bank says it is not yet able to guide investors on the impact."As we make progress towards resolving several previously disclosed regulatory compliance investigations, we expect to recognise additional provisions in the 2H18 result, noting there are significant uncertainties in determining a provisioning outcome at this time," Thorburn told investors in a trading update lodged with the ASX."These additional costs will be excluded from the expense growth guidance of five to eight per cent for the financial year 2018."In its half-year accounts NAB identified at least five specific contingent liabilities where the likely financial impact on the bank was difficult to forecast.These included three investigations into the bank's wealth management business that are examining overcharging, the provision of non-compliant advice and fee-for-no-advice gouging. In addition to these issues, the bank has admitted to problems with its anti-money laundering systems, which might have led to flawed reporting of customer transactions to AUSTRAC.Thorburn did not indicate whether all of these long-running compliance problems would be resolved this financial year, electing to leave the meaning of "several" in his statement open to interpretation.Banking analysts appear to be losing patience with the bank over its decision to delay until yesterday the disclosure of the additional regulatory expense burden.Goldman Sachs analyst Andrew Lyons told investors in a research report that he was disappointed at the timing of the disclosure."We are disappointed that NAB did not cater for a larger regulatory/compliance spend buffer in its prior FY18/medium term cost guidance given there was already fast building momentum on this theme when guidance was originally provided," he told clients.Lyons expects NAB's earnings per share this year - excluding the unquantifiable impact of the additional provisioning - to slide materially.According to Lyon's forecasts, the bank is expected to generate EPS of A$2.14 this year compared to $2.40 in 2017.Thorburn, who last week made another rehearsed video apology to customers following more damning evidence heard at the royal commission, yesterday acknowledged the impact of the hearings on his decision making."The royal commission is challenging us with its focus on where we have let customers down," he said."We are determined to respond and become a better bank through living our purpose and values every day."Such rhetoric, heard often in recent months, did little to help NAB's financial performance in the June quarter, with unaudited cash earnings falling by three per cent to $1.65 billion compared to the corresponding period last year.The bank attributed the