THE SNP’s claim rejoining the EU would boost UK revenues by £30 billion a year is “not unreasonable”, financial experts have said.

In its analysis of the SNP’s General Election manifesto, the Institute for Fiscal Studies (IFS) concluded the figure is roughly what they would expect to see if Brexit was to be reversed.

David Phillips, an associate director at the IFS, said: “In the seemingly unlikely event that the UK did rejoin the EU within the next parliament, this would not be an unreasonably high figure for the eventual boost to revenues."

The SNP launched their manifesto in Edinburgh on Wednesday with a key pledge to “deliver independence”, protect public services and secure NHS investment.

The IFS added that the SNP’s demands for further tax devolution including National Insurance contributions to Scotland are a “sensible idea”.

READ MORE: In full: John Swinney's SNP election manifesto launch speech

However, Phillips seemed to suggest devolving all income tax would be “complex” and devolving VAT could create “trade barriers”.

He said: “Devolving income tax on savings and dividends is a sensible idea, as is devolving National Insurance contributions.

“However, devolving all income tax rules would add complexity for some taxpayers and the tax authorities.

“And VAT is a particularly tricky tax to devolve, potentially creating trade barriers between Scotland and the rest of the UK, with reforms to VAT in Scotland also complicating the system.”

Elsewhere, the IFS said the SNP’s suggestion of providing an additional £18bn for "unprotected" UK government department budgets by 2028-29 to prevent real-terms cuts is “within the range (£10 to £20bn) that we have previously warned such departments would need to avoid cuts under existing spending totals.”.

Phillips seemed to cast doubt though on whether the SNP’s calls for increased NHS spending in England would actually result in a £1.6bn boost to NHS funding in Scotland.

READ MORE: Everything the SNP manifesto says about Scottish independence

He said: “The SNP wants the UK government to top up NHS spending in England by £6bn to fund higher pay, and then by a further £10bn from 2025-26 onwards.

“This would be on top of the 3.6% real-terms increases we have previously estimated would be needed to meet the English NHS’s long-term workforce plan and would be a genuinely significant funding boost.

“The SNP says this would generate an extra £1.6bn for the Scottish Government, which it proposes to invest in the Scottish NHS. But because some of the increases in spending in the rest of the UK would be funded by income tax rises that wouldn’t apply in Scotland, the Scottish Government’s own funding would not increase by as much as the SNP appears to assume.”

During the launch of the manifesto, Swinney confirmed an SNP victory in the General Election would be taken as a mandate to ask Westminster for a second independence referendum.

Swinney said he believed his party already had a mandate for independence from the pro-Yes majority delivered by the 2021 Scottish Parliament elections.

Speaking at the Patina events centre in Edinburgh on Wednesday, Swinney said: “I believe the best way for Scotland to become an independent country, in a way that will address all of the democratic questions, the important questions, is for there to be a referendum.

“That’s what I think is the right way to do it so that will be the purpose of the negotiations that I would take forward in the aftermath of the election.”