Scotland cannot afford to reverse all of the welfare cuts being imposed by Chancellor George Osborne, Deputy First Minister John Swinney has conceded.

The Finance Secretary said it was "highly unlikely" he could find the cash to shield people north of the border from the impact of austerity measures.

And he said he could not offer any guarantees that they would be reversed if the SNP was in charge of an independent Scotland.

Research by IPPR Scotland suggests Scotland's poorest households could be more than £500 a year worse off in 2020 as a result of tax and benefit changes made in the most recent UK Budget.

The package included highly-controversial cuts to tax credits.

Mr Swinney told the BBC that the Scottish Government would continue to find the resources to give "significant assistance" to those affected - as it had in the case of changes such as the so-called "bedroom tax".

But he said a real-terms reduction of expenditure of 10% since the 2010 general election left the Holyrood coffers short.

"I estimate that the cumulative loss of tax and benefit changes will be of the order of about £6 billion," he said at the start of the party's conference in Aberdeen.

"If you are saying to me, can I find £6 billion within the expenditure available to the Scottish Government to reverse all of those decisions, I think that it is highly unlikely."

Asked whether that could be different in the case of Scotland taking full control of spending, he said: "All governments have to run a sustainable budget."

"What we would aim to do is put in place a welfare system that was fair and affordable based on what we inherited when Scotland became independent.

"We would have to deal with the situation as we found it."