Three environmental activists who became the first people to be jailed for an anti-fracking protest in the UK are to appeal against their sentences amid growing anger over their “excessive and extraordinary” punishments.

Last week, Simon Roscoe Blevins, 26, and Richard Roberts, 36, were sentenced to 16 months in prison, and Richard Loizou, 31, was given 15 months after a jury at Preston crown court convicted them of causing a public nuisance.

The men were charged after taking part in a four-day protest that blocked a convoy of trucks carrying drilling equipment from entering the Preston New Road fracking site near Blackpool in July last year.

Kirsty Brimelow QC, the head of the international human rights team at Doughty St Chambers, who is leading the appeal on a pro bono basis, said: “We are applying to the court of appeal for expedition of the appeal. We are fortunate in this country that there is this option. The core submission in this case was made at Preston crown court – that it is wrong to lock up peaceful protesters.”

On Saturday, friends, family and supporters of the three men will stage a solidarity demonstration outside HMP Preston, where they are being held. Planton Loizou, a former tour operator and the father of Richard Loizou, will attend his first political protest in more than 40 years.

“It’s pointless putting them in prison, because what this has done is turn me and his mother and the rest of the family into activists,” he said. “I was a Conservative through and through for the first 32 years of my voting life. My wife wasn’t and I didn’t listen to her and that was a mistake.”

Rosalind Blevins, a former scientific researcher, said she had been expecting her son, Simon, to receive a fine or community service. “He didn’t hurt anyone, assault anyone, intimidate anyone or even verbally abuse anyone, nor did he damage any property,” she said. “I’m proud of him for daring to stand up for what he believes in. I know him to be a fundamentally good person.”

Preston New Road has been a focal point for protests since October 2016, when the government overturned a decision by Lancashire county council and gave the energy firm Cuadrilla consent to extract shale gas at two wells on the site.

More than 300 protesters have been arrested there since Cuadrilla began building a fracking pad in January 2017. The company said on Friday that fracking would start next week, but the high court issued an injunction blocking the work from getting under way until a hearing on Wednesday.

On 25 July 2017, the three men climbed on to the cabs of lorries driving towards the site and stayed there for up to four days. Fellow protesters threw blankets, food and water up to them. Another man, Julian Brock, 47, also took part in the protest and was given a 12-month suspended sentence after pleading guilty to causing a public nuisance.

The action caused the road to be closed for around nine hours until police established a contraflow. During the trial, the jury heard evidence from residents who said their lives were significantly disrupted by the protest, and that local businesses suffered a loss of trade. In mitigation, the defence presented the judge, Robert Altham, with statements from residents who supported the protest.

In sentencing the men, Judge Altham said they had viewed the public as “necessary and justified collateral damage”. He said they posed a high risk of reoffending and could not be rehabilitated as “each of them remains motivated by an unswerving confidence that they are right”.

The sentences have been condemned by environmental campaigners, human rights groups and politicians. Kate Blagojevic, the head of energy at Greenpeace UK, said the men deserved “our gratitude and not a prison sentence”, while Dave Timms, the head of political affairs at Friends of the Earth, said the sentences were “disproportionate and harsh”.

The shadow chancellor, John McDonnell, has called on the government to intervene in the case, describing the imprisonment of peaceful protesters in “a supposedly democratic and civilised society” as unacceptable.

On Wednesday, more than 20 MEPs from the Greens/European Free Alliance group stood together at the European parliament in Strasbourg to express their solidarity with the group. And more than 1,000 academics have signed a letter calling for a parliamentary inquiry of the sentences.

Speaking during the sentencing hearing, Brimelow – who was born in Preston – said the right to freedom of speech went beyond “simply standing and shouting”, and extended to non-violent direct action. She said if jailed, the men would probably be the first environmental activists to be imprisoned for protesting since the mass trespass on Kinder Scout in the Peak District in 1932, which marked the beginning of the right-to-roam movement.

Campaigners have previously received jail terms for breaking court orders and injunctions. In 1993, seven activists were jailed for 28 days for breaking a high court injunction by invading the construction site of the M3 at Twyford Down in Hampshire.

“Everybody knows that if you engage in non-violent civil disobedience then you’re likely to be arrested,” said Kevin Blowe, a coordinator of the Network for Police Monitoring. “But there is a precedent that has been set that follows up from the Twyford Down cases in ‘93, which is that if you’re not involved in a violent action and are acting on conscience, the courts will balance that against any disruption that may take place. So most people, if they are convicted, get a conditional discharge and a fine, they don’t go to prison.”

Lawyers and activists say the Preston case is the latest example of a crackdown on anti-fracking activity, which has involved the increasing use of injunctions by companies seeking to stop demonstrators from slowing down their work.

While fracking is effectively banned in countries including Germany, France, Scotland and Ireland, the UK government announced plans earlier this summer to make it easier for companies to obtain permission to carry out exploratory drilling in England. The business secretary, Greg Clark, said “safe and sustainable exploration and development of our onshore shale gas” was important as North Sea gas production declined and the country became more reliant on imports.

Mike Schwarz, a senior consultant at the law firm Bindmans who has represented Greenpeace for more than 20 years, said the decision to charge the men with the offence of “public nuisance” – a common law offence that carries a maximum sentence of life in prison – was inappropriate.

“I don’t think it is appropriate to use this charge when there are settled, targeted, specific criminal offences [including obstruction of the highway and aggravated trespass] that naturally fit the actions of protesters … And it’s difficult to think of a reason why the prosecution have gone for public nuisance in this case – other than there being a rush of testosterone or an undue haste to do the bidding of business – but obviously they are upping the ante by doing that.”

A Crown Prosecution Service spokesperson said: “After reviewing a file provided by Lancashire police, we decided that there was sufficient evidence and it was in the public interest to prosecute four men with causing a public nuisance.”