Image copyright PA Image caption Net annual migration is currently 230,000, but UK government policy is to slash that number

The UK government's aim of cutting net migration to the tens of thousands could cost Scotland's economy up to £10bn from 2040, according to the Scottish government.

The target was set by David Cameron in 2010, but has never been met.

Annual net migration to the UK is currently 230,000.

Scotland's external affairs secretary, Fiona Hyslop, said a dramatic reduction in that number would be "catastrophic" for Scotland.

But the UK government insisted it would put in place an immigration system that works in the best interests of the whole of the UK - including Scotland - after the country leaves the EU.

And it has said the public is in favour of lower immigration, and has insisted that all future decisions about immigration would be evidence-based.

Ms Hyslop is to unveil a Scottish government paper on Wednesday afternoon that sets out a range of scenarios for future migration, including the UK government's objective of cutting it to the tens of thousands.

The paper suggested that even if the UK government only reduces migration as a result of the end of freedom of movement for EU workers, Scotland's economic growth would be £5bn a year lower from 2040 - 4.5% lower than it would have been otherwise.

It said this would compare to a UK-wide fall of only 3.7%, which it said demonstrated Scotland's greater reliance on migration.

Ms Hyslop said: "While some of these dates and figures may seem a long way off, the decisions the UK government takes in the next few months on the future of migration policy will have a long-term effect that it will be hard to reverse."

"Some sectors of our economy are already finding it harder to secure the workers they need as a result of the UK's decision to leave the EU.

"That makes it all the more important to have the powers to set a tailored migration policy based on the unique needs and circumstances of Scotland, to ensure we protect and enhance future economic growth."

The paper is the first in a series aimed at providing evidence and building a consensus for more powers for the Scottish Parliament, to tackle specific and long-standing challenges, and to address the impact of Brexit.

'Based on evidence'

It will set out the importance of migration to Scotland's economy, Scotland's needs within a UK migration system, and options for Scotland to secure more powers over migration to better support its economy and society.

A Home Office spokesman said: "After we leave the EU, we will put in place an immigration system which works in the best interests of the whole of the UK.

"Decisions about our future immigration system will be based on evidence, which is why we have asked the independent Migration Advisory Committee to assess the economic and social impact of EU citizens in all parts of the UK.

"We are engaging with and considering the view of all stakeholders - including the Scottish government and businesses in Scotland."

It also said there would be an implementation period after Brexit to avoid a "cliff edge" for businesses, and that EU citizens already working in the UK will be able to apply for settled status so they can stay.

Last month, MPs on the Home Affairs Committee called on the UK government to cut its "tens of thousands" migration target.

It said the failure to meet the target "undermines" public trust, and argued that immigration policies should instead consider the UK's needs "and humanitarian obligations".