Pacemaker Press 23/1/2017 Michelle O'Neill is announced as Sinn Fein's new northern leader by senior members Martin McGuinness and Mary Lou McDonald at Stormont. Michelle O'Neill is to replace Martin McGuinness as its leader north of the border. Pic Colm Lenaghan/Pacemaker

Mrs O’Neill, who was the agriculture minister from the scheme’s inception in 2012 until it was closed to new applicants in February 2016, has consistently denied she was aware of how generous the subsidies were.

However, a report emerged on Friday claiming that the department under her watch organised almost 60 workshops “for farmers interested in the Renewable Heat Incentive”.

The article said documentary evidence details how several officials from Mrs O’Neill’s department stressed the financial benefits of the scheme.

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Mr Ford said the revelation called into question Sinn Fein’s knowledge of the RHI scheme.

“This situation does not look good for either the Department or Michelle O’Neill as Minister at the time,” Mr Ford said.

“A serious question has been raised by this revelation – namely, when did she and her Department become aware of the serious problems within the RHI scheme?

“While on the surface it may well be as simple as a Government Minister promoting a scheme from another Department, the critical issue is what Michelle O’Neill knew and when, if her Department was alerted to the flaws, and whether she knew about those flaws when the Economy Minister closed the scheme, claiming it was a victim of its own success.