AN INDEPENDENT Scotland would need to attract an extra 24,000 people per year to meet the Scottish Government's economic targets, Alex Salmond has confirmed.

For the first time yesterday the First Minister put a figure on the level of net immigration - the difference between the number of people settling in the country and those leaving - that would be required to boost tax revenues and maintain public spending in the years to 2030. He unveiled the plan as the Scottish and UK governments clashed over the financial impact of independence on the general population.

Mr Salmond said a Yes vote in September's referendum would bring an "independence bonus" worth £1000 to every Scot.

But Danny Alexander, the LibDem Chief Secretary to the Treasury, said the "Union dividend" of remaining in the UK was worth £1400.

On a critical day for both sides in the referendum campaign, the Scottish Government also downgraded its oil forecasts, confirming that an independent Scotland would start life in worse financial shape than the rest of the UK.

The First Minister's immigration announcement is against a backdrop of success for Ukip in the European elections after the anti-EU party campaigned to limit the number of people allowed to live and work in the country.

A survey last week showed seven out of 10 Scots agreed with Ukip's policy.

Policies to boost immigration were previously published in the Scottish Government's independence White Paper. If Scots vote Yes in September, ministers plan to introduce an Australian-style points-based system to make it easier for skilled workers to move to Scotland. They would also encourage overseas students to work in Scotland by providing special visas, and believe many expat Scots would be tempted to return as a result of independence.

Yesterday Mr Salmond sought to play down the scale of immigration required to offset a projected fall in the working- age population over the next two decades and boost tax revenues. He said the figure of 24,000 was only 2000 higher than average annual net immigration between 2001 and 2011.

He said: "I think to increase the working-age population through net migration of 2000 additional people a year compared to experience of the past 10 years is an entirely reasonable prospective, and is very realistic to achieve."

However, critics pointed out the years from 2001 to 2011 witnessed higher than usual levels of immigration as Poles and other new EU nationals gained the right to move to Scotland.

The UK Government estimated future net immigration to Scotland at 15,500 per year. The Institute for Fiscal Studies think tank forecast 7000.

Mr Alexander said the Scottish Government's target was equivalent to welcoming a city the size of Edinburgh to Scotland every 20 years.

Scottish Conservative MSP Alex Johnstone said: "If a separate Scotland has a notably different immigration policy to the rest of the UK, as the Scottish Government targets dictate there will be, there will have to be border controls."

Meanwhile, business tycoon Sir Tom Hunter expressed dismay at the lack of clarity as the camps clashed over the financial impact of independence.

He said: "The 28th of May was supposedly the day we the voter were to gain clarity on the economic impact of independence in or out of the Union. Sadly that day is passing and we've had none of the sort.

"What has been presented to us today is farcical, and how any undecided voter could pick through the claims and counter-claims and make any sense of them is well beyond me. We as voters have been disrespected."