The federal government’s policy of shipping off visa overstayers and people who failed the strict new character tests to Christmas Island led to a surge in immigration detainees on Christmas Island in the months leading up to last week’s riot in the detention centre.

Immigration Minister Peter Dutton has estimated that rioters damaged up to $10 million in property in the Christmas Island detention centre after a two-day stand-off between Serco, the Australian Federal Police and detainees. According to asylum seeker advocates, the death of an Iranian asylum seeker who had escaped the detention centre triggered the riot. According to the Department of Immigration and Border Protection, the “disturbance” was caused by a minority of detainees who were in the centre for overstaying their visas or whose visas had been cancelled on character grounds.

Shortly before Tony Abbott’s cabinet reshuffle in November last year, legislation passed in parliament to tighten the character grounds for visas under section 501 of the Migration Act. Under the new character grounds, a person’s visa will be cancelled if he or she has a “substantial” criminal record or has been found guilty of a sex offence involving a child.

A “substantial criminal record” now means someone serving 12 months in jail, rather than two consecutive years for the same offence, as was the case before the changes. Now, a person who commits a crime that has a six-month jail sentence and another crime that has a six-month jail sentence would have that counted as total jail time of 12 months. A person serving time with concurrent sentences would also have those sentences added together in determining whether a visa should be cancelled.

The legislation also removes the requirement that there be a “substantial” risk the visa holder poses a danger to the Australian community as grounds for cancellation. The new wording gives as grounds for cancellation that there be a “risk” that a visa holder might pose a danger to the Australian community.

Since then, so-called 501 cancellations have boomed. Over the 2014-2015 financial year, 580 visas were cancelled under the character provisions of section 501 — an increase of 600% on the previous financial year.

The number of people who overstayed their visas or had their visas cancelled and were taken to immigration detention was 3889 for the full last financial year. As of the end of June, there were 892 people in these categories in immigration detention.

Most of the people who have their visas cancelled under section 501 remain in onshore detention, the department confirmed to Senate estimates in October. As of the end of September, 288 detainees were in either Villawood, Maribyrnong, Yongah Hill or one of the other onshore detention facilities, whereas just 94 detainees with 501 cancellations were on Christmas Island.

A total of 52 of these detainees were New Zealanders. Overall, there were 226 New Zealanders in immigration detention, with 196 subject to visa cancellation on character grounds.

Dutton claims only “serious” criminals were sent to immigration detention. Since he became the Minister for Immigration, Dutton — a former Queensland police officer — has had a focus on cracking down on people on visas involved in motorcycle gangs. The influx to Christmas Island since Dutton began his war on bikie gangs does provide some insight into how the composition of detainees has changed dramatically.

501

The number of detainees on Christmas Island has fallen significantly since its peak of over 2000 under the previous government. In part responding to the Australian Human Rights Commission report on children in detention in February this year, the government has moved a number of children and families from the Christmas Island detention centre into the community. As a result, the population detained on Christmas Island had been decreasing substantially in the months leading up to June this year, reaching a low of 80 detainees at the end of April. But after the 501 changes, the population of the detention centre began growing again, up to 285, all male, detainees at the end of September.

The proportion of people held in detention centres (not just Christmas Island) for overstaying a visa as a percentage of the total detainee population rose from 41% to 49% between the end of April and the end of September this year.

Refugee Action Coalition’s Ian Rintoul told Crikey that the dynamic on Christmas Island had shifted significantly.

“Christmas Island is now four to one, 501s to asylum seekers.”

The Immigration Minister told 2GB’s Ray Hadley on Thursday that, as of now, there were 199 detainees on Christmas Island. He claimed 113 of these were serious criminals:

“It [includes] 113 with serious criminal offences, including manslaughter, sexual offences against children, people that had been involved in armed robbery, people that had been involved in grievous bodily harm, serious assault otherwise. [Some] people that had serious histories including outlaw motorcycle gang members. People who had been involved in those activities and everybody knows that they’re the biggest distributors of drugs in the country and they involve themselves in extortion.”

That contradicts what New Zealand Labour MP Kelvin Davis has said, stating in October, before the riot, that Kiwi detainees he met there were not serious criminals. There is also the case of Ian Wightman, who is on Christmas Island facing deportation to the UK. He has had his visa cancelled under section 501 after serving 15 months in jail for starting a scrub fire. Wightman has lived in Australia for 50 of his 51 years.

But if they are all such hardened criminals, as the government claims, why aren’t they automatically deported? Many appeal their deportation, and the government holds them in detention while those appeals are processed. Rintoul says anecdotally, the amount of time people on cancelled visas remain in detention varies.

“There’s one guy who is Afghan who came very early in the ’90s … he was moved just before the riots, but he’d been there four years. It depends a lot on the nationality because sometimes they find it easier to send others [back].”

He says this year several 501s have been moved from Yongah Hill onto Christmas Island, where the department says the facilities are designed to cope with higher-risk detainees. New Zealanders tend to remain in detention for a shorter amount of time, Rintoul says, because of co-operation with the NZ government, but people of other nationalities can remain up to 12 months if there is difficulty negotiating the deportation with the person’s country of origin.

“The problem is often the appeals process isn’t the longest part, it’s often the countries don’t want them back. Often protracted discussion of whether they should, and negotiations for passports. There was one US guy who took 18 months [to deport] even after he’d exhausted his appeals process here. He did longer in Villawood than he did in Silverwater [jail] for fraud.”

Dutton confirmed on Thursday that seven of the men allegedly involved in the riots — five New Zealanders, a Tongan and an Afghan — had been transferred to a prison in Western Australia, with more expected to follow. He said some were appealing, which would delay their deportation.

The cost for Serco — which is now being investigated by the government for its handling of detainees on Christmas Island in the lead-up to the riot last week — to operate the centre is expected to go down as the population in detention decreases. At last reporting it was costing the government $318 million per year to operate.

The Department of Immigration and Border Protection is not currently answering media questions regarding Christmas Island. Inquiries on the number of 501 detainees on Christmas Island, as well as a nationality breakdown, time spent in detention, and other information around detainees on Christmas Island were referred to the office of the Immigration Minister on Friday. Dutton’s office did not respond by deadline Monday.