SPENDING promises in the run-up to the next Holyrood election must be independently assessed, one of Scotland's biggest trade unions has warned.

Unison, which represents public sector workers, said political parties should agree to have their 2016 manifestos audited because of the severe budget cuts facing Scotland immediately after the election.

Some of the deepest public spending cuts of George Osborne's eight-year austerity programme will come in financial years 2016/17 and 2017/18, according to analysis of the UK Government's spending review.

Dave Watson, Unison's head of campaigns in Scotland, said: "At a ­Scottish level and a UK level the really bad news is being put off until after the ­elections. We are extremely concerned at the impact of the cuts still coming down the line.

"An independent audit of manifestos would be worthwhile, though we accept it would not be easy."

He suggested the proposed ­independent Scottish financial body equivalent to the Office for Budget Responsibility (OBR), which is being considered by MSPs, could undertake the task in 2016.

The call follows growing concern among trade unions about the scale of spending cuts facing Scotland.

Unison yesterday demanded an end to the council tax freeze following fresh warnings of thousands of local authority job cuts and as Scottish Government ministers became embroiled in a row over library closures in Moray.

The PCS civil service union also condemned the UK Government's austerity measures as it launched a referendum strategy based around protecting public services.

The CPPR think tank, based at ­Glasgow University, recently claimed in a study that there would be smaller cuts to the Scottish budget in financial years 2014/15 and 2015/16 compared with the last four years. However they will be followed by real terms cuts of 3.2% in 2016/17 and a further 3.6% in 2017/18.

They are worse than any year apart from 2011/12, when spending was slashed by 5.1% in real terms - and appear to be unavoidable.

Labour's Shadow Chancellor Ed Balls has promised "iron discipline" on spending if his party wins in 2015.

The SNP have indicated a similar determination to tackle the deficit in order to set up an oil fund if Scotland votes for independence.

Finance Secretary John Swinney has promised to maintain popular policies such as the council tax freeze, free prescriptions, free bus passes for the over-60s and free university tuition up to 2016.

Scottish Labour, meanwhile, have faced intense criticism for establishing a panel of MSPs, MPs and experts - dubbed the "cuts commission" by the SNP - to assess their affordability and fairness in the light of looming cuts.

The commission's recommendations are expected to form the backbone of the party's 2016 Holyrood manifesto.

At Westminister, Labour have argued for party manifestos to be audited by the OBR before the 2015 General Election.

A Scottish Labour spokesman said: "All political parties have a duty to the people of Scotland to face up to the crisis in public spending which is looming beyond the referendum, whatever the result.

"Ahead of the 2016 election, we will set out an ambitious manifesto for Scotland that will protect the most vulnerable and ensure the country's finances are on a sustainable footing.

"We are confident our plans will stand up to any scrutiny."

An SNP spokesman said: "The SNP always present fully costed manifestos - as evidenced by our record in government in funding the council tax freeze, no tuition fees, free personal care, and the bus pass for the over-60s, all within Holyrood's fixed budget.

"Therefore, while we are happy to listen to constructive suggestions, the key issue for the 2016 election is whether we will be electing an independent parliament - with full control over Scotland's resources, and the powers to chart a different economic course - or another devolved parliament which would be at the mercy of Westminster cuts."

The CPPR's analysis showed a real terms cut, based on current prices, of 18.9% in the Scottish budget between financial years 2009/10 and 2017/18.

The total cut is equivalent to £5.9 billion when inflation is taken into account.

By the end of the 2013/14 financial year, only 57% of the total real terms cut will have been imposed.

In their report, the CPPR said the £2.7bn of real terms cuts still to be made to ­budgets for everyday services in Scotland will be "increasingly hard to accommodate".

Chancellor George Osborne's spending review extended his austerity programme from six years to eight.