Around 40 percent of Scots plan to vote for independence in this year's referendum, according to a poll on Thursday which showed a three-point rise in support for an end to the country's 307-year-old-union with England, UK edition of Reuters reports.

The poll, carried out by Panelbase, showed that 45 percent of those questioned intended to vote against Scottish independence, a decline of two points from the last equivalent survey.

Scotland, which has a population of just over 5 million and whose territorial waters are the source of much of the North Sea's oil and gas, will vote on September 18 on whether to leave the UK.

Fifteen percent of the respondents said they were still undecided.

Support for Scottish independence appears to have gathered pace over the last month, according to three different polls, as those opposed to independence have stepped up their campaign.

Last month the British government warned that Scots could lose the pound if they vote to leave the UK, and high-profile business leaders including the bosses of oil giants BP and Shell have expressed concern about Scotland going it alone.

For the independence poll, Panelbase surveyed 1,036 people over the week to March 14, having last asked 1,022 people the same question in February. The question was: "How do you intend to vote in response to the question: Should Scotland be an independent country?"

All Scottish residents aged 16 or over can vote in the referendum and if a majority vote in favour of the move, Scotland will become an independent country on March 24, 2016.