london british prime minister david cameron is gearing up to make a strong business case for scotland to remain within the united kingdom after 200 business leaders signed an open letter backing independence he will use a key speech at the confederation of british industry cbi annual dinner in glasgow to bolster the campaign against scottish independence ahead of the referendum on september 18 camerons speech later today will come with a warning that one million jobs could be put at risk by scottish independence because the country is better off as part of something bigger highlights from his speech have been released as open letters signed by hundreds of business leaders on either side of the debate began doing the rounds cameron will say 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 this success doesnt 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 while the no group which includes signatories from a variety of businesses including banking mining engineering food whisky and technology claims the business case for scottish independence has not been made lobby group business for scotland said economic facts and figures support scottish independence scottish first minister alex salmond had challenged cameron to name a single jobcreating power certain to come after a no vote he has set out six jobcreating powers for scotland that he said were guaranteed with a yes vote in next months referendum control over the business tax system control over finances control over air passenger duty control over employment policy control over trade policy and control over immigration policy the cbi has been forced to scale back its dinner after the electoral watchdog ruled it constituted a campaign event up to 700 business leaders usually attend the meeting but it is understood only around 230 will attend this year so as not to flout electoral commission rules it marks a major intervention just weeks before the crucial independence referendum and most opinion polls currently suggest the proposal is set to be rejected