LONDON (REUTERS) - Just under one-third (29 per cent) of Scots plan to vote for independence in this year's referendum, according to a poll on Thursday that also found 42 per cent intended to vote against.

But the TNS poll also found another 29 per cent were still undecided ahead of the Sept 18 vote to decide whether Scotland, which has a population of just over 5 million and is a source of North Sea oil, should end its 307-year-old union with England and leave the UK.

The percentages are virtually the same as in the previous two TNS polling agency votes carried out since the New Year.

The poll of 996 adults was carried out between Jan 28 and Feb 6.

That was before the three main parties at Westminster - who oppose a break-up - had rejected the idea of an independent Scotland sharing the pound.

It was also before European Commission President Jose Manuel Barroso said it would be "difficult if not impossible" for any break-away state to join the EU.

"The debate on independence has stepped up a gear in the last few days," said Tom Costley, head of TNS in Scotland.

"Opinion in Scotland showed little change over the last few months, with a relatively high level of Don't Knows, and our polls have consistently shown that people are looking for more information on which to make their decision," he said in a statement.

"It may be that the recent activity, especially the firm statement by the anti-independence parties on the future of the pound, will stimulate more debate, bring out more information and help undecided voters to make up their minds."