Malcolm Turnbull was last night forced to defend controversial changes to Australian citizenship laws on ABC’s 7.30 program.

The Prime Minister was grilled by host Leigh Sales about what prompted the sudden overhaul, announced on Thursday by the Federal Government.

Under the changes, successful applicants will need to have been a permanent Australian resident for four years, demonstrate greater English language proficiency, prove their commitment to the nation and honour “Australian values”, though it remains unclear how the latter will be assessed.

Opening the interview on Thursday evening, Sales posed a simple, pointed question to the Prime Minister: “What is the actual problem you are trying to fix here?”

“What we’re doing is reinforcing the citizenship which is at the foundation of our nation, ours the most successful multicultural society in the world…” Mr Turnbull replied.

“If it’s so successful, what’s the problem?” said Sales.

Pressing the Prime Minister on the motivation for the changes, Sales raised a speech he gave on multiculturalism in February, in which he reportedly made no reference to issues around English language proficiency or "Australian values" among new citizens.

"What's changed in the 10 weeks since then, other than your growing need to shore up your political stocks?" she said.

Prime Minister Turbull dismissed the question as "cynical".

“I’m disappointed that you’re so cynical but I’m used to it,” he said, going on to argue that "the vast majority of Australians" support the need for action on those issues.

"It's been very carefully considered, I can assure you," he added.

The new measures, which according to Turnbull have been developed by cabinet over "months", will require applicants to demonstrate that they have integrated into Australian society, for example by joining clubs or by providing evidence that their children are enrolled in school.

A more stringent, stand-alone English language test will also be introduced, which will include "reading, writing and listening" components.

Discussing that topic during the interview, Sales posed the example of Westfield CEO Frank Lowy, a man who had "little English" when he arrived in Australia in 1952, and would have not likely achieved citizenship under the new requirements.

"Is that the sort of Australian we’re happy to miss out on?” she said.

The Prime Minister again dismissed the question, and said “perfectly fair and in their interest” for applicants to have a competent level of English.

On the issue of "Australian values", Sales questioned whether Christianity's unequal treatment of women would adhere to them - "wives submit to your husbands, and so forth," she said.

Prime Minister asserted that "respect for women and children, and respect for the equal rights of women" are central to Australian society.

“I’m surprised you’re challenging this on the ABC, but there it is," he added. "I don’t think your heart’s in it actually, Leigh. I think you agree with me.”

The proposed changes will be introduced to parliament following public consultation, which closes on 1 June 2017.

The government has said new measures will apply to those applying for citizenship on or after 20 April 2017, the day they were publicly announced.

Several members of the opposition have criticised the announcement, including Senator Penny Wong who accused the Prime Minister of making the changes primarily for his own political purposes.

"This looks to me like the change you make when you want people to notice," Senator Wong told AM.