Multi-millionaire retired businessman Alan Dunlop has called on Conservatives to unite once the contest concludes.
Mr Dunlop rejoined the Tory Party following the announcement that Boris Johnson was stepping down as prime minister.
He said: “Whether you back Rishi Sunak or Liz Truss isn’t the issue. Party activists have to row in behind the winner, our new prime minister, to ensure the Conservatives win the next general election.
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“The need for party unity – all speaking from the same script – is paramount. We cannot have division or any ill-feeling. We have to present a strong, one-nation message with conviction and produce commitments designed to re-energise the economy.”
The Shankill Road-born former steel importer continued: “Preserving the Union has to be the priority. There is a determined effort under way in Northern Ireland to wreck the Union and we must be prepared to see off that threat.
“We are all better within the Union rather than in a united Ireland where, as we have seen, there is little respect afforded to unionism and our Britishness. We have to start talking up the tangible benefits of remaining in the Union to counter the fiction that’s expressed by republicans.”
Mr Dunlop also raised the prospect of a Labour government taking power after the next general election.
He said: “Nationally, the thought of Sir Keir Starmer in government is frightening. Just imagine the wholesale damage Labour, with its crackpot ideas, would do to the country overall and you will quickly see the necessity for a strong, fighting-fit Conservative Party.
“The Conservatives know how to govern. Liz Truss or Rishi Sunak will provide a clear direction of travel and I know that whoever succeeds Boris Johnson will be single-minded and focused on steering our country to a better place.”
Last October Mr Dunlop resigned from the Tories claiming the national party was reluctant to organise properly in the Province.
Ms Truss and Mr Sunak are scheduled to hold a leadership debate in Northern Ireland on August 17. The day before the pair will debate in Scotland with both visits signalling their commitment to the unity of the UK.