By Jenny Gross And Jason Douglas 

LONDON--Three polls on support for Scottish independence released Saturday suggested that next week's referendum is too close to call.

A survey released late Saturday by ICM Research for the Telegraph newspaper put support for independence seven percentage points ahead of support for staying in the United Kingdom, the Telegraph reported. But two earlier polls put pro-union support narrowly in the lead.

The polls come ahead of a Thursday vote on whether Scotland should end its 307-year union with England. The ICM survey of 705 people said 49% of those surveyed supported independence, 42% were against and the rest were undecided. On Friday, ICM published a survey that put unionists narrowly in the lead.

Two other surveys had similar results and put support for the union ahead. A poll by Opinium for the Observer newspaper showed support for staying in the union at 47%, while support for independence was at 43%. The rest were undecided.

Another Saturday survey by pollster Survation for the pro-union campaign put support for maintaining the union at 47% and support for independence at 41%, with the rest undecided or unwilling to reveal their voting intention.

Recent polls have shown an uptick in support among Scots for independence, but most still put the pro-union camp in the lead. Up until a month ago, support for staying in Britain had been strongly in the lead.

Blair McDougall, director of the pro-union Better Together campaign, said Saturday's polls showed that every single vote counts.

"There is no room for a protest vote when so much is at stake with the irreversible decision we will make," Mr. McDougall said in a statement late Saturday.

U.K. Prime Minister David Cameron and other top politicians this week stepped up their campaigning, canceling their schedules in London to travel to Scotland to urge Scots to reject independence. Mr. Cameron made an emotional plea to voters and told them he cared deeply about Scotland staying in the U.K. Mr. Cameron is expected to speak in Scotland on Monday.

Businesses this week also voiced concerns about independence. Lenders Royal Bank of Scotland Group PLC and Lloyds Banking Group PLC said they planned to move their legal headquarters to England in the event of a vote for independence. In addition, executives of companies such as BP PLC and Royal Dutch Shell PLC have expressed concern in recent weeks.

Alex Salmond, the leader of the Scottish National Party, has said London politicians bullied these companies into speaking out against Scottish independence. He and his nationalist supporters say Scotland would be much better off if it has an independent government with full control over taxes and economic policy.

Write to Jenny Gross at jenny.gross@wsj.com

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