Scottish pensions would be in danger if voters decide to split from Britain this year, a senior British minister will say on Friday in the government's latest attempt to persuade Scots to reject independence.

Danny Alexander, second-in-command at the finance ministry, will say pensions held with Scottish firms would not be protected by British state guarantees in the event of independence and that a new Scottish-only backstop for savers would be costly and less secure.

Alexander's warning comes little more than six months before a referendum on whether Scotland should sever its 307-year tie to the rest of Britain, which the British government is campaigning hard to discourage.

An Ipsos-Mori poll this week showed 32 percent support for independence, 57 percent against and 11 percent undecided.

London has focused much of its campaign so far on fiscal and economic issues. Having ruled out the prospect of sharing sterling with an independent Scotland, the government turned on Friday to the impact of independence on Scots' savings.

"A vote for independence opens the flood gates to a sea of uncertainty on currency, rates and regulation - all of which puts the value of those life savings at risk," Alexander will say, according to excerpts of his speech.

The Scottish National Party hit back.

"An independent Scotland will be more able to afford pensions than the rest of the UK and all pensions will be paid in full after independence," said Nicola Sturgeon, deputy first minister of Scotland's devolved government.

Last week insurance and pensions firm Standard Life, which has been based in Scotland for 189 years, became the first major company to warn it could partly move out of the country in the event of independence.

Alexander - a Scot - said other firms from Scotland's well-developed financial services sector could follow.

"With a different regulatory system and a different currency and different pensions protections, many companies would have no choice but to relocate their businesses," he said.

Alexander also denied claims by Scottish nationalists that London would soften its stance against a currency union after a vote for independence.

"Our decision - taken in the best interests of Scotland and the rest of the UK - is final," Alexander said. "No matter how much of a racket they make, it isn't going to change."