LONDON (AFP) - British Prime Minister David Cameron made a last minute appeal to Scottish voters on Wednesday to reject independence in a referendum next week as polls showed the campaign on a knife edge.

Writing in the Daily Mail newspaper ahead of a surprise trip to Scotland by rival Westminster party leaders in a push to preserve the 300-year-old union, Cameron warned against independence as a "leap into the dark".

"The United Kingdom is a precious and special country. That is what is at stake. So let no one in Scotland be in any doubt: we desperately want you to stay; we do not want this family of nations to be ripped apart," Cameron wrote. "If the UK breaks apart, it breaks apart forever. So the choice for you is clear: a leap into the dark with a Yes vote, or a brighter future for Scotland by voting No. You can have the best of both worlds in the UK."

Cameron said that by voting "No", Scots would be choosing staying in the union but with greater devolved powers for the Holyrood parliament over borrowing, taxation and spending.

The Conservative party leader said he supported a timetable for the transfer of powers outlined by the three main unionist parties in response to a surge in support for independence.

Cameron's Conservative party is not popular in Scotland, with only one member of parliament out of 59, and the prime minister kept a low profile in the campaign until a shock poll showed the pro-independence side ahead for the first time.

Reports in British media have said the prime minister might be forced to resign by rebels in his party if he fails to stop Scotland leaving the union. Latest polls showed a collapse in support for the union from a month earlier and put the "Yes" and "No" sides neck and neck, causing the pound to tumble to a 10-month low and shares in Scotland-linked companies to fall.