Scottish first minister says prime minister right to be worried as recent showed 46% of Scots in favour of independence

Alex Salmond, Scotland's first minister, has said that President Obama's decision to intervene in the debate on Scottish independence showed how alarmed David Cameron was about the prospect of the no camp losing.

In an interview on the BBC's Andrew Marr show, Salmond said he was surprised to hear Obama suggest that he was opposed to Scotland breaking away from the UK because in the past the American government has made it clear it was remaining neutral in the contest.

"But then, of course, David Cameron has been begging everybody internationally to say anything to help with his travails at the moment," said Salmond, referring to reports that Cameron asked Obama to speak out on Scotland before the two leaders appeared at a joint news conference in Brussels on Thursday, where the question was raised.

Salmond said Cameron was "right to be worried" because a recent Populus poll showed 46% of Scots in favour of independence, and 54% against, when don't knows were excluded.

"Perhaps on the Richter scale of presidential interventions, this was pretty mild," Salmond added. "[Obama] hopes that the UK will be strong and united as an ally. Well, if Scotland becomes independent, America will have two allies in these islands, not one."

Obama said that ultimately this was a decision for the Scots. He also said that the UK seemed to have worked "pretty well" and that Washington had "a deep interest in making sure that one of the closest allies that we will ever have remains a strong, robust, united and effective partner".

Although all the three main Westminster parties are proposing further devolution in the event of Scotland voting no, Salmond said the Scots would be "foolish" to rely on these promises.

"The only guarantee of getting more powers is to vote yes on 18 September," he said, pointing out that before the 1979 referendum, in which the Scots voted for devolution but not by enough to pass the threshold required for devolution to take place, the Tories had suggested that a no vote would not rule out further devolution.

"Scots voted yes and, as it was, we didn't get devolution and what we got was 18 years of Margaret Thatcher. So I think, having had that experience, we'd be very foolish to rely on promises from unionist parties."