Colin Farmer hit by stun gun in Chorley, Lancashire, by PC Stuart Wright, who mistook his white stick for a samurai sword

A police officer has been asked to apologise to a blind man whom he shot with a Taser when he mistook his white stick for a samurai sword.

Colin Farmer, 64, was hit by the stun gun in Chorley, Lancashire, by PC Stuart Wright in October 2012 as he walked to his local pub.

Farmer, who thought he was suffering a stroke, was then handcuffed by the officer, who had responded to reports of a man in the town centre with a sword.

He was walking away from PC Wright at the time and posed no threat, an investigation by the Independent Police Complaints Commission (IPCC) found.

Farmer was handcuffed while lying on the ground and was not released until the arrival of another officer, whom Wright told: "I think I've got the wrong person," said the IPCC.

A report from the police watchdog found Wright failed to take reasonable steps to ascertain if Farmer was carrying a sword before he discharged the Taser.

He had used a level of force that was "unnecessary and disproportionate to the circumstances" and caused further distress to Farmer by detaining him in handcuffs despite it being obvious he had the wrong man, it added.

Wright also ignored instructions and radio transmissions about how to deal with the incident, and failed to comply with local and national guidelines on the use of a Taser.

Lancashire constabulary held a two-day disciplinary hearing that concluded on Tuesday, following a recommendation from the IPCC that the officer had a case to answer for gross misconduct.

That meeting concluded that Wright was not guilty of gross incompetence but should be issued with a performance improvement notice and that he be told to apologise personally to Farmer.

The IPCC commissioner, James Dipple-Johnstone, said: "Farmer was subjected to what must have been a terrifying ordeal. Our view was that Wright could and should have listened to instructions from his force controller and taken greater steps to ascertain whether Farmer was the sword-carrying man that had been reported by members of the public and when he realised his mistake should have acted quicker to put things right.

"There is public concern about use of force, and, particularly, Taser. Incidents such as this do little to ease that concern. I hope that the personal apology to Farmer allows the officer to reassure him that he will learn lessons from these events and that the improvement plan for the officer and measures taken by the force to improve its training and communications prevent further incidents such as this."

In a statement, Lancashire constabulary said: "The officer was dealt with under stage 3 of the Police (Performance) Regulations 2008 for gross incompetence by a panel made up of Assistant Chief Constable Tim Jacques, Chief Supt Richard Goodenough-Bayly and Mr Ashley Judd, the constabulary's head of human resources.

"The panel found that the officer failed to perform his duties to a satisfactory standard on October 12, 2012, though his actions did not amount to gross incompetence.

"The officer will be issued with a written improvement notice and be required to demonstrate specific performance improvements over a set timescale. Additionally, the officer has expressed considerable regret over this incident and arrangements will be made for him to offer a personal apology to Mr Farmer."

Jacques added: "First and foremost I would like to sincerely apologise to Farmer on behalf of the constabulary for what happened that evening and the resulting distress and anxiety he undoubtedly suffered.

"The officer made a dreadful mistake when he discharged his Taser, but was acting on a reasonable and honestly held belief that his actions were necessary to protect the public. The officer did not perform his duties to a satisfactory standard but we did not feel that this amounted to gross incompetence.

"In addition to the findings relating to the individual officer, this investigation has raised a number of issues for the constabulary to consider including the training given to officers carrying Taser."

Farmer was unavailable for comment. Last year, his lawyers said they had lodged a civil claim at the high court for damages on grounds of assault and battery, false imprisonment and suffering inhumane and degrading treatment.

Last August, the Crown Prosection Service said it would not take any criminal action against the officer as there was insufficient evidence to prove he had not been mistaken.