Jeremy Hunt has insisted plans to allow high-flying business people to become British ambassadors will not lead to conflicts of interest in the posts.
The Foreign Secretary unveiled the move in a speech in which he announced a programme to recruit an additional 1,000 diplomatic staff in the UK and abroad.
With Brexit just five months away, he told an audience at the Policy Exchange think tank "we must reinvigorate and expand British diplomacy".
But his plan was criticised by a Civil Service trade union, which said it risked undermining UK interests abroad.
Asked about potential conflicts of interests in allowing business tycoons to represent Britain abroad, Mr Hunt said: "Our intention is one or two posts every year, no more than that, might go to people who have been truly outstanding in another field. But, it will go through the proper Foreign Office recruitment process. There will be absolutely no question of conflict of interest."
A Foreign Office spokesman said the move to recruit ambassadors from other fields "builds on a university outreach programme launched earlier this year which aims to encourage applications from under-represented groups".
British ambassadors are traditionally civil servants, often with a long career in the diplomatic service.
This is in contrast to other countries such as the US, where the president can nominate ambassadors, who then have to be approved by the Senate.
Dave Penman, general secretary of the FDA union which represents senior civil servants, said: "The role of a diplomat in representing the UK's interests abroad is much broader than simply trade, which is why they go through years of training and develop such a range of skills. That expertise already includes international trade. To solely focus on this area risks undermining the UK's interests and influence given the complexities of international relations.
"Diplomats are made, not born and the UK's interests are best served by a professional diplomatic service."
Sir Christopher Meyer, a former British ambassador to the United States, said the role of ambassador was wider than just trade and investment, encompassing areas such as media relations and a cultural role.
He told the BBC: "This is a good idea in principle. The question is how would it actually work in practice. In Jeremy Hunt's speech there is a little bit of reinventing the wheel there. I can remember back in the distant past and when David Owen - Lord Owen - was foreign secretary, he introduced the policy of 'interchange' and that would put people from the business sector into the diplomatic service and vice versa.
"Did it ever really take off? I don't think so, but in all my career the Foreign Office was always open to the idea of recruiting outside the professional cadre."
He added that one obstacle had been the "modest" pay compared with what was on offer in the private sector.
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