David Cameron will plead with Scottish voters on Thursday not to abandon one of the "oldest and most successful single markets in the world", after the home secretary, Theresa May, highlighted nerves in the pro-union campaign, warning that it needed to redouble its efforts.
As the
referendum campaign enters its final stage the prime minister will seek to warn wavering voters of the dangers of separating from the UK by raising the prospect that
Scotland's financial services could lose 90% of their business if voters endorsed independence on 18 September.
Cameron will acknowledge that questions over the economy lie at the heart of the referendum campaign when he says that key Scottish industries are underpinned by membership of the UK.
In a speech to the
CBI Scotland conference in Glasgow, he will say that 90% of Scottish financial services' customers live in England, Wales and Northern Ireland, while Scotland's computer gaming industry and its "cutting-edge sub-sea technology" benefit from selling across the UK without transaction costs.
His arrival comes as the Scottish first minister,
Alex Salmond, receives a boost from 150 business leaders who have signed a letter supporting independence. The signatories include
Ralph Topping, the former chief executive of William Hill, and Tom Barrie, managing director of the logistics company
Currie European.
Details of the letter emerged a day after 130 prominent business leaders, including the HSBC chairman Douglas Flint, signed an open letter warning that the case for
Scottish independence had not been made.
Cameron will tell his audience: "This is one of the oldest and most successful single markets in the world. Scotland does twice as much trade with the rest of the UK than with the rest of the world put together – trade that helps to support one million Scottish jobs.
"For some industries, the proportion of trade with the rest of the UK is even higher – 90% of Scottish financial services' customers are in England, Wales and Northern Ireland. Then there's the world-famous gaming industry, cutting-edge subsea technology and life-saving biomedicine – all selling far more outside Scotland than inside.
"This success doesn't happen by accident. It happens because of the skill of people in Scotland and the opportunities that come from being part of something bigger, a large domestic market, underpinned by a common currency, common taxes, common rules and regulations, with no borders, no transaction costs, no restrictions on the flow of goods, investment or people. Ours really is an economy of opportunity."