Supporters of Scottish independence are "deeply misguided" to think the country would do better on the world stage, according to Foreign Secretary William Hague.
The senior Conservative attempted to pick apart the case for Scotland becoming a state in its own right during a speech to an invited audience in Edinburgh, which included consular representatives from other nations.
He said: "I believe that those who say Scotland would be better going it alone with foreign policy are deeply misguided. They claim that the UK's foreign policy and overseas representation is focused too much on status and power and not enough, for example, on trade and investment.
"They argue that our extensive overseas network is merely a legacy of empire, rather than something that serves the interests of the UK's citizens. They say Scotland's core interests will be better served as a separate state. They are wrong on each and every count."
His half-hour speech covered themes including jobs and growth, foreign policy influence, global security and clout within the European Union.
The intervention was dismissed by pro-independence campaigners, who said Mr Hague is attempting to "lecture" Scots.
The Foreign and Commonwealth Office has "never been as focused" on jobs and growth, he said in defence of UK policy. "The Scottish Government has trade offices in 18 countries - many of them in British embassy buildings, working alongside British diplomats," he said. "But as part of the UK, Scotland also has access to UK Trade and Investment, which has more than 1,000 staff in over 100 countries and helped over 500 Scottish companies to export last year alone."
The success of whisky has also been helped by access to British work overseas, he said. Reduced access to the global network would also put Scots abroad at a disadvantage, he claimed.
The widely trailed speech, inside the Merchants' Hall in the capital, ranged over Scotland's shared history with other parts of the UK. Before the visit, he claimed people across the world are baffled by the drive for independence, saying other countries envy Britain's standing. During his speech, standing in front of a large portrait of the Queen, he added culture to the mix, suggesting Scottish values - as part of the UK - helped shape the world. He linked the power of the UK, and the shared English language, to success abroad for sportsmen and women, knitwear and even Harry Potter.
A spokesman for Scotland's External Affairs Minister Humza Yousaf said: "Mr Hague says he hasn't come to make 'threatening noises', but his comments are insulting and patronising. There is huge goodwill towards Scotland across Europe and around the globe, and an independent Scotland will be warmly welcomed on to the international stage, something which will also ensure we have a seat at the top table and are able to make the case directly on behalf of our leading industries and exports."