Deloitte have quit as auditors of financially troubled Rangers after staff received threatening and intimidating messages over a two year period.

In a letter distributed to Rangers International Football Club plc shareholders, Deloitte say the messages came from “anonymous third party sources” during 2013 and 2014.

In a separate letter to shareholders James Blair, the RIFC company secretary said: “The board is disappointed that Deloitte has chosen to resign due to acts which occurred in 2013 and 2014 whilst RIFC was under different stewardship.”

South African businessman Dave King and allies took control of the RIFC board from allies of Sports Direct tycoon Mike Ashley in a shareholders vote at an extraordinary general meeting on March 6.

The Deloitte letter dated June 19 states: “We have decided that we no longer wish to carry on as auditor to the company.

“During the period of our audit appointment in 2013 and 2014, members of our engagement team and other Deloitte partners unconnected with the audit received threatening or intimidating messages from anonymous third party sources.

“The safety and wellbeing of our staff is of paramount importance, and they should not be subject to this treatment when undertaking their normal professional duties. Accordingly we are resigning as auditors to Rangers International Football Club plc.”

Blair told shareholders there had been “positive discussions” ongoing with “alternative auditors” and that an announcement on an appointment will be made “in the near future”.

The announcement to shareholders comes three months after the latest half-yearly RIFC accounts said that the Rangers holding company had appointed London-based accountants Jeffreys Henry to act as independent reporting accountants after discovering Deloitte had announced an “intention to resign” following the June 2014 audit.

Acting chairman Paul Murray said at the time that the previous board “chose not to announce this nor did they find a replacement”.

At the time the board said it would make “a further announcement on this subject once we have found a replacement firm for Deloitte”.

The board said the financial statement made for the six month period to December 31 2014 was made on a “going concern basis”, saying it was investigating a “number of options” for future finance and had identified a number of potential investors.