Poll shows backing for Scottish independence rising to 40 percent

(Adds BAE Systems comments)

LONDON, March 20 (Reuters) - 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.

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 Sept. 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 (LSE: RDSB.L - news) have expressed concern about Scotland going it alone.

Europe's biggest defence contractor BAE Systems (LSE: BA.L - news) on Thursday became the latest British company to enter the debate.

"It is clear that continued union offers greater certainty and stability for our business," BAE's chief executive Ian King said in the FTSE 100 company's annual report.

BAE, which employs 3,600 people in Scotland, called its interests there "significant".

"In the event that Scotland voted to become independent, we would need to discuss the way forward with the Ministry of Defence and UK government, and work with them to deliver the best solution in those circumstances," King said.

BAE's activities in Scotland include building warships such as Britain's new aircraft carrier HMS Queen Elizabeth.

For the independence poll, Panelbase surveyed 1,036 people over the week to Mar. 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. (Reporting by Sarah Young; editing by Andrew Roche)