Reform UK has said it will launch a private prosecution against the men suspected of being involved in a disturbance at Manchester Airport in July if they are not charged by the Crown Prosecution Service (CPS).

Footage of a fracas at the airport went viral and appeared to show an officer kicking and stamping on the head of Fahir Amaaz, 19, as he and his brother Muhammed Amaad, 25, were restrained by officers.

Further footage, obtained by the Manchester Evening News, emerged days later which showed the immediate lead-up to the incident on July 23, including when two female police officers were hit to the ground before Mr Amaaz was incapacitated with a Taser.

An investigation by the Independent Office for Police Conduct (IOPC) is under way into the incident and nobody has been charged.

A letter to Home Secretary Yvette Cooper signed by the party’s five MPs said: “We have genuine reason to be concerned that in fact, the CPS is awaiting for the IOPC to find some fault with the police officers, which will then give them a reason not to progress charges against the assailants. This is totally unacceptable.”

The letter added: “We are therefore serving notice that if the CPS is not going to charge the assailants, then we will organise a private criminal prosecution against them. We have taken initial advice and have a legal team on standby to progress when required.”

The letter added that the prosecution would be crowdfunded if necessary.

A private prosecution is one not brought by a “prosecuting authority” – one of several public bodies including the CPS with the statutory power to bring prosecutions.

The process involves applying to a magistrates’ court for a summons beginning the prosecution, and if successful, the prosecution can be taken over by the CPS, which can then either continue the case or end it.

Former crown prosecutor Nazir Afzal suggested a private prosecution would be difficult to bring, saying: “A private prosecution faces the same evidential test that a crown prosecution does – namely that a jury, properly directed by a judge, would be more likely to convict than not.

“So if the CPS decides it doesn’t, it’s extremely rare for a court to permit a prosecution by a private party on the same evidence.

“The defence can apply to the court to have it stopped and the CPS can take over any private prosecution and drop it.”

Asked how long Reform would wait before beginning a private prosecution, party chairman Richard Tice said: “Not long, but we are not going to specify exactly.”

The party has previously threatened to sue the company responsible for vetting its candidates at the last election, but no such action has yet begun.

Greater Manchester Police passed a file relating to the disturbance at Manchester Airport to the CPS in mid-August, and four men remain on police bail in connection with the incident.

A spokesperson for the force said: “We have avoided providing ongoing commentary on the case, including releasing footage, to ensure that justice can be served without the risk of prejudicing proceedings.

“We continue to support the officers involved and are committed to getting them justice.”

The average time between a referral from the police and the CPS reaching a charging decision is 46 days, according to the latest available data.

Aamer Anwar, the solicitor representing Mr Amaaz and Mr Amaad, said: “Whilst Reform are often accused of having a precarious grip on reality – this latest diatribe is no more than pathetic grandstanding.

“Whilst some may want to mimic a Taliban system of justice, thankfully in a civilised society we believe in due process, which is not dictated to by the mob.

“If Reform want to pursue a private prosecution, I for one would gladly see them lose thousands of pounds. In the meantime, we will await the outcome of the CPS investigation into my clients but also the GMP officers, and I doubt very much that the CPS will be pressured by the latest rantings of Mr Farage and co.”

A Home Office spokesperson said: “There is no such thing as two-tier policing.

“We expect high standards of conduct from police officers and they must equally be able to carry out their jobs without disruption.

“It is right that the CPS and the IOPC are both able to carry out their investigations independently, without fear or favour.”

A CPS spokesperson said: “We are considering material and are providing advice in relation to a series of alleged criminal offences at Manchester Airport in July this year.

“We are working with Greater Manchester Police and the Independent Office for Police Conduct while their inquiries continue.”