Malcolm Roberts has submitted he is eligible to stay in the Senate because he “honestly but wrongly” believed he had done everything he could to renounce British citizenship through an email that went “into the ether”.

In submissions to the high court released on Friday, the One Nation senator argued that he did not “know” he was a British citizen when he nominated in June 2016 because he did not “believe” he was.

Last week high court justice, Patrick Keane, found that Roberts was a British citizen at the time and that “arguably” the only step he took to renounce dual citizenship was sending a 6 June email that experts agreed “could not be effective as a renunciation” because it was not sent to the UK Home Office.

Keane said Roberts “knew that there was at least a real and substantial prospect” he was a British citizen. In his submissions Roberts dismissed “the fact he appreciated he might be wrong” about being British as “irrelevant”.

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

Roberts said his “subjective belief was that he was only Australian”, despite the fact he travelled on a British passport as a child and did not become an Australian until he was formally naturalised in 1974.

Roberts adopted the central submission of the Turnbull government, which is defending the eligibility of its members and senators Barnaby Joyce, Fiona Nash, and Matt Canavan, that a parliamentarian had to have “voluntarily” acquired dual citizenship to be disqualified.

But the government has submitted that Roberts should be found ineligible because he was naturalised as an Australian and therefore would have been aware he held foreign citizenship before that, which he would then need to renounce.

Roberts submitted his case was “indistinguishable” from the others because he did not know he was British, arguing that suspicion he may have been did not equate to knowledge.

Unlike the other six parliamentarians facing eligibility questions, Roberts said he at least “sensibly appreciated the possibility he might be wrong” about only being Australian, giving him a “stronger [case] than those who profess ignorance and thus did nothing”.

Roberts submitted he “positively rejected the notion of being a British citizen” by attempting to send an email headed “am I still a British citizen?” to the British consulate on 1 May to two addresses that were no longer in use.

After no response to his first email, Roberts emailed those addresses again on 6 June, and another apparently flawed one, australia.enquiries@fco.gov.ukSydney.

“That email was ineffective under British law for the simple reason it was not received by any agent of Great Britain,” his submissions conceded. “It appears to have literally gone into the ether.”

The submissions also conceded the email could not have effectively renounced his citizenship because the address was still wrong, and it did not contain a fee nor a “declaration of truth”.

Roberts submitted he had taken all reasonable steps to renounce his citizenship and “the fact it is easy to identify other steps” he could have taken was “not the point”.

“If there is a reasonable step test then it must be accepted that something less than perfection is contemplated. Otherwise, the question of reasonableness would never arise.”

In their submissions to the high court, former Greens senators Larissa Waters and Scott Ludlam argued “ignorance or wilful blindness” should not be used as an excuse to save parliamentarians in potential breach of the constitution.

In a joint submission they said they were right to resign when they became aware of their dual citizenship status.

“In complying with obligations under the constitution, negligence should never produce a more favourable result than diligence,” they argued.

The Greens submitted it was reasonable to enquire into one’s status as a dual citizen when put “on notice by reason of the person’s foreign place of birth or the foreign citizenship status of that person’s parents or grandparents”.