The level of need for affordable housing in Scotland is double what is currently being delivered, according to a report.

At least 12,000 homes need to be built every year for the next five years to meet demand, three housing associations have said.

Undertaking such a programme would cost £700 million a year, experts commissioned to look into the issue found.

The Scottish Government currently has a target of building 6,000 affordable homes per year.

A report - Affordable Housing Need in Scotland - was carried out by a team from the independent Centre for Regional Economic and Social Research at Sheffield Hallam, Sheffield University and the University of St Andrews.

It was commissioned by Shelter Scotland, the Chartered Institute of Housing (CIH) Scotland and the Scottish Federation of Housing Associations (SFHA), and calls for the biggest house building programme in Scotland since the 1970s.

The three housing associations are calling on all Scotland's political parties to set "ambitious" targets for new affordable housing in their manifestos for next year's Scottish Parliament elections.

The Scottish Government is to consider the report but said it is "already delivering a huge boost to affordable housing provision", with 30,000 properties to be completed by the end of the life of the current parliament.

Graeme Brown, director of Shelter Scotland, said: "The 12,000-a-year target for new affordable homes is the minimum level required to tackle Scotland's housing crisis.

"We are calling on all political parties in Scotland to acknowledge there is a crisis by making the building of new affordable homes a priority in their manifestos for the forthcoming Holyrood elections and use the 12,000 target as a benchmark for their ambitions.

"Politics is about making choices and we have simply got to do more to reduce homelessness in Scotland."

SFHA chief executive Mary Taylor said: "Whilst we acknowledge that the Scottish Government is on track to meet its current target of 6,000 affordable homes over five years per annum, this figure must be doubled to 12,000 in order to meet the growing housing need across the country on top of a backlog of need.

"The research provides evidence of the scale of need. Scottish ministers are already considering recommendations from the subsidy review group earlier this summer which showed a need for increased subsidy."

A Scottish Government spokeswoman said: "We are already delivering a huge boost to affordable housing provision across Scotland by investing over £1.7 billion to build 30,000 affordable homes during the lifetime of this Parliament.

"We will consider the findings of this report and in the meantime continue to support recovery and growth through initiatives like Help to Buy (Scotland) and the Help to Buy (Scotland) Small Developers scheme.

"We are working closely with all sectors to promote the construction of new homes, support jobs in the construction industry and inclusive growth in the wider economy."