The Australian activist who disrupted the 2012 Oxford v Cambridge Boat Race in protest at government cuts has been ordered to leave the country, after receiving a six-month jail term that many thought was severe.

Trenton Oldfield, whose British wife is expecting a child this week and who has lived in the UK for more than 10 years, has had his application for a spousal visa refused. The Home Office informed the 37-year-old that his continued presence in Britain would not be "conducive to the public good" after he swam in front of the crews during the 158th Boat Race on the Thames.

Oldfield, who was given a six-month jail term and served two months in Wormwood Scrubs, told the Guardian he had appealed. "No one was expecting this. I have a tier one visa, as a highly skilled migrant, and I was sentenced to less than a year. The lawyer said I had nothing to worry about because it was less than a year. It feels to me that this is a very vindictive decision, very political and very much an overreaction."

He stressed that his protest was peaceful and non-violent. "Before bringing their verdict, the jury asked the judge if she could be lenient. The probation officer recommended a non-custodial sentence. The sentence was excessive, but the judge also said I have contributed positively to life in this country."

Oldfield, who has no previous convictions, rejected the notion that he might return to Australia. His wife Deepa has never been there and she has relatives in the UK. "We clearly have a life together here," he said. "We work together, we publish books, we run two not-for-profit organisations. Every part of our lives is entangled together here. We are about to have a family."

He told the court that his protest, which halted the race for 25 minutes, was designed to highlight elitism in British society. Before setting out, he wrote a blog setting out his rationale and making clear his plan did not constitute an act of terrorism. "People tell me that on the day of the race, 500,000 people looked up the word 'elitism' on Google. It sparked a debate."

His wife, 36, knew nothing of his intentions. She was abroad and he deliberately hid the plan from her for fear she would be prosecuted as part of a joint enterprise. "We didn't think they would seek to effectively deport him," she said. "We were told that was for violent criminals, major fraudsters and terrorists. Nothing Trenton did approaches that."

She added: "We can't not live and work together. That's impossible. I can't be separated from him. I don't think people will see his sentence and this decision as reasonable consequences from a peaceful protest. It seems to reinforce the point he was making about the Boat Race. Would this be happening if he had disrupted any other event?"

Jailing Oldfield last October Judge Anne Molyneux was critical, ruling that he had acted "dangerously and disproportionately" and exhibited prejudice, but she made no adverse reference to his immigration status.

Oldfield's appeal casts the visa refusal as disproportionate and says it breaches article 8 of the European convention on human rights, guaranteeing the right to a family life. Among those supporting Oldfield is his MP, Rushanara Ali, who represents Bethnal Green and Bow in east London. "He has served his sentence and now his right to family life is being undermined," she said. "I don't condone what he did, but it seems disproportionate to say that someone whose offence was to disrupt the Oxford v Cambridge Boat Race is a threat to our security, whose presence is not conducive to the public good."

Supporters also claim a pattern of victimisation. Oldfield originally faced a public order offence before the charge was increased to public nuisance, with the potential for life imprisonment. In the interim, the Tory MP Michael Ellis had used a meeting of the home affairs select committee to suggest to the Met commissioner, Bernard Hogan-Howe, that Oldfield would better be charged with an offence that might offer a custodial sentence. Hogan-Howe said that was being considered.

The campaigning journalist John Pilger, who signed a petition protesting at the judicial authorities' treatment of Oldfield, said the home secretary's stance was ridiculous. "He is not a criminal or a terrorist. He was a protester acting on principle, whether or not you agreed with his action. What the Home Office is really saying is that all forms of protest are now potentially criminalised," Pilger said.

Mitch Mitchell, a member of the campaign group Defend the Right to Protest, said: "The authorities are cracking down harder and harder against anyone who raises a voice."

The Home Office spokesman said: "Those who come to the UK must abide by our laws."