ScotTISH housing associations will warn today that the so-called bedroom tax is unfair, arbitrary and incompetent, at the launch of a major report on its impact.

Mary Taylor, chief executive of the Scottish Federation of Housing Associations (SFHA) said tenants and landlords had stepped "through the looking glass" due to the policy of limiting housing benefit for people deemed to have an unused spare room.

She said: "We have to make sure people are not penalised for failing to occupy something that doesn't exist, or isn't available to them.

"How can we argue to someone that their benefit will be cut by up to 25% unless they downsize when there is nowhere for them to move to? Lewis Carroll would be proud of the policy."

Each housing association is expecting to lose up to £608,000 a year in unpaid rent depending on its size, the new report shows.

"We are already seeing a spike in arrears and we expect more down the line," Ms Taylor added.

The study on the early impact on social landlords of the Coalition Government's underoccupancy penalty, as the bedroom tax is officially known, is launched today at the SFHA's annual conference in Glasgow.

It shows 90% of social landlords expect arrears to rise, with 38,000 tenants having to find £21 million to cover the shortfall between rents and their housing benefit.

The report also reveals housing associations are being inundated with requests for help from tenants making claims for emergency funds from councils.

Speaking today, Ms Taylor will say: "We are seeing affected tenants race to access the limited £10 million available in Scotland for discretionary payments."

She called for the housing benefit changes to be repealed but said the Scottish Government must do more to help, with housing associations already experiencing an increase in rent arrears.

"This could compound the already significant financial challenges faced by social landlords, since the Scottish Government cut funding for investment in social housing by 53%," she said.

"If housing associations and co-operatives are going to be able to meet Government targets to build new homes, then the Scottish Government must restore the funds cut from social housing."

Housing Minister Margaret Burgess is expected to defend Scottish Government spending plans at the conference. She said it has taken every chance to boost investment in housing, adding: "By the end of April we had allocated £200 million additional funding for housing supply."