While those in favor of independence depict a sovereign Scotland as a wealthy place of opportunity and renewal, those opposed talk of the harm the breakup might do to jobs, prosperity and stability. The anti-independence former Prime Minister Gordon Brown, himself Scottish-born, said on Tuesday that separation from the rest of Britain would be a “messy and expensive and costly and difficult divorce.”

“The effect of Sept. 18, if you vote yes, is to end every single last remaining link that exists, the connections we have, with our friends, neighbors and relatives,” Mr. Brown said.

But Nicola Sturgeon, Scotland’s pro-independence deputy first minister, declared during a visit to a steelworks, “My feeling going around the country is that we’ve got an enormous sense of growing confidence in Scotland, and a feeling that, having come this far, we should keep control of the future of this country where it is just now, in our hands.”

Ms. Sturgeon said an independent Scotland would “continue to be part of the family of nations that make up the British Isles,” and added, “We will work closely and cooperatively with our friends across these islands, but we’ll do so on the basis of equality, we’ll do so knowing that we’re responsible for the decisions that shape our future.”