Malcolm Roberts has pleaded with the High Court to let him keep his Senate seat, arguing he “honestly but wrongly” believed he had done everything possible to renounce his British citizenship.

The One Nation senator, in his official submission filed on Friday, believes his case is no different from that of the five other politicians facing possible disqualification who have the backing of the federal government.

In fact, Senator rubbished legal arguments by the Commonwealth that some of the politicians embroiled in the dual citizenship saga should be let off because they simply did not know they were foreigners.

The submission noted that Senator Roberts’ wife, “on whom he places great reliance”, was suffering a serious illness between April and August 2016 and had also spent a large time in the US looking after her then-dying mother.

Earlier in the week, the Commonwealth’s submissions to the High Court argued Deputy Prime Minister Barnaby Joyce, deputy Nationals leader Fiona Nash, former Nationals minister Matt Canavan, South Australian senator Nick Xenophon and former Greens senator Larissa Waters should be saved because they would not have known they were dual citizens.

His legal team claims it’s irrelevant that Senator Roberts understood there was a substantial prospect that he was a British citizen at the time of nomination.

“The question is: what did he believe his citizenship to be? He believed he was Australian and that is the end of the matter,” the submission says.

Nevertheless, his lawyers argue he took all reasonable steps to renounce his British citizenship – namely, emails in May and June to non-existent addresses.

He admits, however, they “have literally gone into the ether” and were ineffective under British law.

But his case goes to his “state of mind” – that he had resolved his suspicions about possible foreign citizenship by sending the emails.

Those “honest and legitimate” attempts were sufficient to disengage section 44 of the constitution, “thus he has been and remains qualified to sit in the Senate.”

He is the final member of the “Citizenship Seven” to submit his arguments to the High Court on why he should keep his spot in Federal Parliament.

Last week, the High Court ruled Senator Roberts was a dual citizen when he nominated as an election candidate.

The full bench will hear his case, and those of Deputy Prime Minister Barnaby Joyce, Nationals senators Matt Canavan and Fiona Nash, crossbencher Nick Xenophon and resigned Greens senators Scott Ludlam and Larissa Waters, in Canberra from October 10.

Who actually breached the Constitution?

The Commonwealth argued only Senator Roberts and former Greens senator Scott Ludlam had breached the constitution.

But the One Nation senator’s lawyers disagreed, and panned the Commonwealth’s arguments.

“His case is indistinguishable from most of the other referents now before the court, in particular, those of Mr Joyce, Senator Canavan, Senator [sic] Waters, Senator Nash and Senator Xenophon,” Senator Roberts’ lawyers argued.

“The ultimate submission by the Attorney to the effect that people who just do not know they are a citizen of another country and because of that do nothing about it are somehow in a better position vis-a-vis s 44 (i) than someone who acknowledges the possibility and honestly tries to reject any other citizenship is as alarming as it is illogical.”

Lawyers for Mr Ludlam and Ms Waters have also criticised the Commonwealth’s arguments, suggesting it is relying on a complex interpretation of the constitution to save the Coalition’s own members.

The High Court’s full hearings in the citizenship cases are on October 10-12.

– with ABC’s Matthew Doran, AAP