“I mean, I suspect we could have an army of 120,000, of which 30,000 might be robots, who knows?” Carter said, although he stressed he was not setting any particular target in terms of future numbers.

Investment in robot warfare was to be at the heart of the planned integrated five-year defence review, whose future was thrown into doubt after the chancellor, Rishi Sunak, postponed the cross-government spending review to which it had been linked last month.

Carter said negotiations with Downing Street and the Treasury about salvaging the multi-year defence funding settlement were “going on in a very constructive way” – as he lobbied in public for a long-term financial deal.