Northern Ireland should have been part of the Great Britain Renewable Heat Incentive scheme, an inquiry into how the local version of the initiative became mired in controversy heard.
John Mills, who managed the DETI (Department for Enterprise, Trade & Investment) energy team, told the inquiry that in his view the Northern Ireland Civil Service did not have the capacity to manage a scheme as complex as RHI.
His preference would be for Northern Ireland to be part of a properly resourced UK-wide scheme run from Whitehall.
"There was no 'off switch' in the RHI scheme," he said in his witness statement. "If I could change one thing about the RHI it would be not to do a separate Northern Ireland scheme."
Mr Mills also said that the DETI Minister at the time the RHI scheme was implemented, Arlene Foster, had not pushed for the scheme to go live without cost controls, as had previously been suggested.
He said such a view, which he himself had at one time held, was "completely incorrect," and was based on an assumption, not on any evidence.
Earlier, Trevor Cooper, who was finance director of DETI, which brought forward the RHI scheme, was asked to explain why the department chose to implement a subsidy-based scheme instead of a grant-based scheme, when a grants-based scheme would have been much cheaper for the public purse.
The answer was that in the short term, the subsidy scheme was cheaper to set up and administer - despite having much greater long-term cost implications.
Mr Cooper told the inquiry that the Treasury in Whitehall would not have approved the upfront spending required to establish and run a grants-based scheme
He said he believed the grants model was a "much bigger risk" than the subsidy scheme because it had to be designed from scratch.
The inquiry is now in recess for a fortnight.
It will resume its sittings on April 10.
The RHI Inquiry - which is chaired by former judge Sir Patrick Coghlin - was established to examine the design, governance, implementation and operation of the Renewable Heat Incentive scheme from its conception in 2011, and to examine efforts to control the costs of the scheme.