Writing off decades-old debts from the "poll tax" is part of efforts to make local taxation fairer, the Deputy First Minister has said.

John Swinney said the levy introduced by Margaret Thatcher's government - which was know officially as the Community Charge - was a "defunct" and "discredited" tax.

With the Scottish Government now having brought forward legislation to write off the sums still owed, he said this would help "ensure that the poll tax is consigned to history once and for all".

After last year's independence referendum sparked an upsurge in voter registration, former first minister Alex Salmond announced the debts would be scrapped amid fears some councils would try to use the extra information they had to chase outstanding payments.

The Community Charge Debt (Scotland) Bill is now progressing through Holyrood.

Mr Swinney said: "This Bill is one step the Scottish Government is undertaking to make local taxation fairer."

An independent commission set up in partnership with Scotland's councils to look at alternatives to the current council tax would also contribute to this, the Deputy First Minister said.

He stated: "The Government decided to act because we were concerned an appetite had been expressed among certain local authority leaders to use the information that was gathered from voter registration for the independence referendum to reactivate the pursuit of many of the outstanding arrears.

"We felt that sat uncomfortably with what was a wide appreciation through the country for the upsurge in democratic participation during the referendum."

He added: "We also wanted to make it crystal clear that local authorities were absolved of their obligations to collect poll tax debt."

Mr Swinney said he understood some people who had paid the levy at the time were opposed to the debt write-off but he added: "In this case we are dealing with a tax that lasted for four years and was the subject of massive political controversy and enormous political disruption, and was concluded more than 20 years ago."

He insisted that ministers "believe the poll tax is a defunct tax, it is a discredited tax" despite the "affection for which it seems to be held on the Conservative benches".

Mr Swinney told how 10 local authorities had given up chasing the debts and said there was "no practicable possibility" of councils collecting the £425 million that is still owed north of the border

"Almost all of the £425 million can no longer be collected," Mr Swinney told MSPs.

"In the 20 years that have passed since the community charge was abolished, and replaced with the council tax, many people have moved home, moved away from Scotland, married, changed their name or are sadly deceased. They could not now be traced and pinked to a debt."

Instead, councils will receive a share of £869,000 from the Scottish Government in 2015-16 - which is the amount that Mr Swinney said councils could still reasonably expect to recover.

The Bill is being accelerated through Holyrood so it can be in place for the start of the next financial year.

Ministers consulted with the local government body Cosla and councils "who are the only bodies that could be adversely affected by our proposals," Mr Swinney said, although there was no public consultation.