THE Immigration Minister has ordered his department to allow British policeman Peter Threlfall and his family into Australia.

Chris Bowen's intervention followed revelations in The Advertiser yesterday that the family had been denied visas because Mr Threlfall's 25-year-old step-daughter, Sarah, has autism.

Mr Threlfall last night likened the backflip to winning the lottery.

He said SA Police had told him his original job offer as a constable in Ceduna would be honoured, and he hoped to be in Australia by September. "This is unbelievable. I just can't get over it," Mr Threlfall said from London.

"I knew it was achievable, it was just getting the right person to overturn this bad decision, but it was so hard to get to that person. My wife is in tears - we are so happy."

The Threlfalls were originally denied visas because an Immigration Department medical officer deemed Sarah's condition would place a burden on health- care and community services in Australia.

This was despite the fact Sarah has two jobs and plans to study as a hairdresser in Australia. Disability advocates last night applauded Mr Bowen's intervention, but demanded the immediate scrapping of the "discriminatory" policy behind the original decision.

Intellectual Disability Association of SA chairman David Holst and Greens immigration spokeswoman Sarah Hanson-Young both called on the Government to bring immigration policies into line with a 2010 parliamentary report on the issue.

"This case, like similar ones in recent years show why there must be reforms to the health waiver requirement," Ms Hanson-Young said.

"The Greens call on the Government to fulfil the recommendations from the Enabling Australia 2010 parliamentary inquiry report, particularly raising the 'cost threshold' of the health requirement and those criteria affecting family migration."

Opposition immigration spokesman Mitch Fifield said there needed to be greater flexibility in cases such as that of the Threlfalls.

Mr Threlfall hoped his case would help ensure policy change after the Immigration Department deemed Sarah could be a $500,000 burden on Australian healthcare and social services, despite assurances she was employed, largely self-reliant and rarely sought medical assistance in London.

"You can't adopt a hypothetical situation without taking into account any positives," he said.

A spokesman for Mr Bowen said after learning about the case he had asked the department to "facilitate entry for the family".

Migration Institute of Australia state president Mark Glazbrook said cases such as this were too common.

"There is this general assumption that certain conditions will have a high cost and because of that the visa will be refused, even when you can get strong evidence to say there shouldn't be a high cost," he said.

The Threlfall family received a deluge of support from readers of AdelaideNOW and The Advertiser's Facebook page yesterday.

"That's disgusting! Let them in and stop the discrimination against disability," one reader commented.

Autism Advisory and Support Service president Grace Fava applauded the decision, saying people should not have to live with a label.

SA Police Assistant Commissioner Bryan Fahy said SAPOL would honour its original employment offer.