BEIJING, Sept. 15  -- As Scotland is scheduled to hold an independence referendum on Thursday, London urged and expected Scots to reject it and save the union that lasted for 307 years.

The leaders of the three major British political parties jointly pledged on Tuesday to give Scotland more powers if voters reject independence.

The pledge was signed by Conservative British Prime Minister David Cameron, opposition Labor party leader Ed Miliband, and Liberal Democrat Deputy Prime Minister Nick Clegg and published on leading Scottish newspaper the Daily Record.

The leaders agreed to give the Scottish parliament "permanent and extensive new powers" and reaffirmed a timetable for new powers they announced last week.

They noted that a "No" vote will deliver faster, safer and better change than separation.

Cameron jetted into Aberdeen in northeast Scotland on Monday to urge Scots to reject independence and vote "No" in a last-ditch bid to save the union.

Cameron told local Conservative activists that a "Yes" vote is a decision that means Scots can't go back and "the United Kingdom would be no more" there.

"This is the week that could change the United Kingdom forever," said Cameron, while admitting that "many people across Scotland will vote Yes."

"Scottish independence would not be a trial separation, but a painful divorce," he said. "Please don't break up this family of nations" and "Let's stick together," he appealed.

Pledging major new powers on tax and spending to Scotland, Cameron said that "we want you to stay, from head, heart and soul" and "we are better together."

"Please vote to stick together, vote to stay, and vote to save our United Kingdom," the British prime minister added.

Meanwhile, thousands of people gathered at Trafalgar Square in London on Monday, urging Scottish voters to reject independence and stay within the United Kingdom.

However, earlier Monday, Scottish First Minister Alex Salmond appeared at Edinburgh Airport and joined a group of prominent pro-independence business people.

Salmond described the referendum as a "once-in-a-lifetime opportunity for Scotland," insisting that "a positive campaign will always beat the scaremongering campaig."

On Sunday, Queen Elizabeth urged Scots to think "carefully" ahead of Thursday's referendum after attending Church near Balmoral Castle in northern Scotland.

Last week, a number of financial services firms, including Deutsche Bank, threatened to head for the exit door if Scotland voted "Yes" to independence. Retailers John Lewis and Aldi both warned Scottish shoppers would face higher prices.

In October 2012, Cameron and Salmond signed the Edinburgh Agreement, allowing Scotland to hold an independence referendum on the question of "Should Scotland be an independent country?"

The White House said on Monday that the Obama administration prefers a "united" Britain.

"This is a decision for the people of Scotland to make," spokesman Josh Earnest told reporters at a daily news briefing. " We certainly respect the right of individual Scots to make a decision."

"But, you know, as the president himself said, we have an interest in seeing the United Kingdom remain strong, robust, united and as an effective partner," he added.