Alex Salmond claims an independent Scotland needs an extra 24,000 migrants

Alex Salmond’s independence blueprint aims to attract thousands more immigrants, who could use Scotland as a back door to England.

The Scottish National Party say they would ’celebrate’ more people arriving from overseas, reversing what they claim is years of ’depopulation’.

Mr Salmond says Scotland needs an extra 24,000 immigrants a year to fill jobs and bankroll the welfare system for ageing Scots, but without tough border controls many could use it as an easy route into England and Wales.

Data from the Office for National Statistics (ONS) suggests that over the long term Scotland can expect net migration of only 15,500 a year, on current trends.

But Mr Salmond’s target of 24,000 means he will have to attract an extra 9,500-a-year, or 190,000 over two decades, by adopting different immigration rules to the rest of the UK.

Mr Salmond has admitted the thousands of extra foreign workers are needed to fund the state pension in Scotland.

The ratio between pensioners and workers is far worse in Scotland than in the UK as a whole, meaning the cost of funding pensions is borne by fewer people.

Pete Wishart, the SNP’s home affairs spokesman, wrote on the party's website: ’We plan a controlled points-based system to support the migration of skilled workers for the benefit of Scotland’s economy.

’An independent Scotland will have an inclusive approach to citizenship and a humane approach to asylum seekers and refugees.’

He complained about ’anti-immigrant rhetoric’ and claimed Scotland currently has to ’lump inappropriate Westminster immigration laws, and we are constantly told that they must become even more restrictive to protect us from the various ‘floods’ of ‘foreigners’ who are to erode our way of life’.

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He added: ’In Scotland, when we see an increase in our population given our history of depopulation, we celebrate the good news. At Westminster it couldn’t make the politicians more miserable.’

The SNP hopes for an independent Scotland to join Common Travel Area (CTA) which dates back to the 1920s and allows free movement between the UK, Ireland, the Channel Islands and the Isle of Man.

The official white paper for independence states: 'We plan to remain part of the CTA which means that there will be no border controls, and you will not need a passport to travel to other parts of the UK, Ireland, the Channel Islands and the Isle of Man.'

An illegal migrant tries to step into a truck going to the UK in the French port of Calais. David Cameron wants to see migration cut - but Alex Salmond insists Scotland needs more labour from abroad

An independent Scotland operating an open border migration strategy would jeopardise an English government's attempt to curb the number of migrants settling

However, Mr Salmond also wants to have a more relaxed immigration policy than that adopted by Westminster, raising the prospect of Scotland being used as a back door route into the UK.

The SNP plans to lower the current financial maintenance thresholds and minimum salary levels for entry to Scotland, and to reintroduce a 'post-study work visa'.

It means it would effectively have a more open immigration policy than the rest of the UK, requiring controls at the border.

The Prime Minister wants to see net migration cut to 100,000 a year - but is currently running at almost 250,000

The changes would take effect from 24 March 2016 when Scotland would formally become an independent country.

Earlier this year Scottish Secretary Alistair Carmichael accused the SNP of having 'two fundamentally contradictory propositions'.

'First of all they say we can be part of the CTA, which [would be] an open border between Scotland and the rest of the United Kingdom, and at the same time they say they will have a widely divergent immigration policy.

'You can have either of these things, but you cannot have them both. My challenge to the Scottish Government is to explain which of these it is going to be.'

Mr Carmichael said the SNP's immigration proposals are 'radically different' and would be 'incompatible' with the CTA.

It means travellers heading south could be forced to pull over and undergo lengthy Calais-style identity checks on 21 roads that cross the border, including the A1, A68 and M74.

Rail passengers would also need to prove they had a right to enter the country before boarding a train leaving from Glasgow, Edinburgh or Aberdeen for England, in a similar time-consuming regime to Eurostar journeys from France.

A UK Government analysis paper, launched in January, also revealed that lorries and vans could be inspected at the English border if Scotland becomes independent amid fears of alcohol and tobacco smuggling.

A spokesman for Yes Scotland said: 'Existing UK passports can continue to be used as normal until they expire.