The Scottish Charity Regulator (OSCR) is calling for changes to the legislation governing health boards in Scotland in the wake of its investigation into financial mismanagement at NHS Tayside.

An interim report into alleged misspending of endowment funds says OSCR has concerns about all 15 boards across Scotland.

In a letter to the public audit and post-legislative scrutiny committee, David Robb, CEO of the OSCR, said the structure outlined in the NHS (Scotland) Act 1978 "gives rise to an inherent and unavoidable conflict of interest" between the health boards and endowment charities.

He added that, in the view of the OSCR, changes to the act are required to place the issue "beyond doubt".

The inquiry was launched after it was revealed earlier this year that in 2014 the board of NHS Tayside used more than £2m donated to its endowment fund to cover running costs such as funding new technology.

These "core" costs would normally be funded from its core budget.

The endowment fund is made up of donations from the public or bequests in wills.

An outcry over the incident led to a clear-out of management at the health board, with its chairman, chief executive and director of finance leaving in the months that followed.

The inquiry is looking into whether or not NHS Tayside had the power within its own constitution to suspend the endowment fund's policy and procedures on a temporary basis, to allow for the money to be used for an E-health initiative.

It has interviewed all board members and key participants from the January 2014 decision in a bid to decide whether the board acted in the interests of the charity and whether members exercised the level of diligence required of a charity trustee.

The next stage of the inquiry will decide if there has been misconduct under the Charities and Trustee Investment 2005 Act and whether the regulator will take enforcement action against individual board members.

As part of its inquiry, the OSCR analysed the activities and governance of all 15 NHS endowment funds in Scotland.

The report states: "The pictures that has emerged from our analysis is generally positive and encouraging, and we hope this will help reassure existing and potential supporters of these charities.

"Most have separate endowment sub-committees in place to review grant applications in details and make recommendations to the board in line with clearly defined delegated authority limits.

"However, I should note that this was also the case in Tayside at the time of the decisions made in early 2014."

It adds: "There are a few minor issues of departure from good practice, on which we are engaging with individual charities."

A full report will be published at the end of November.