Colin Farmer, a blind 61-year-old, was shot in the back with a 50,000-volt stun gun by police in Chorley, Lancashire. ITN

An innocent blind man was shot in the back with a 50,000-volt Taser by police after they mistook his white stick for a samurai sword.

Colin Farmer, 61, was hit after reports of a man walking through Chorley, Lancashire, early on Friday evening, with a sword. He said he initially thought he was being attacked by hooligans when he was struck by the Taser.

The matter is being investigated by the Independent Police Complaints Commission (IPCC) after Farmer made a complaint to the force.

Farmer, who used to run an architects' practice, was on his way to meet friends at 5.45pm and was walking in Peter Street near a restaurant. "I was just walking along and I heard some men shouting really angrily and thought I'm going to get mugged. I didn't know any police were here.

"The Taser hit me in the back and it started sending all these thousands of volts through me and I was terrified. I mean I had two strokes already caused by stress. I dropped the stick involuntarily and I collapsed on the floor face down."

He added: "I was shaking and I thought 'I'm going to have another stroke any second and this one is going to kill me. I'm being killed. I'm being killed'."

Farmer, who has suffered two strokes, the most recent requiring two months in hospital in March, was fearful he would suffer another stroke.

"I walk at a snail's pace. They could have walked past me, driven past me in a van or said 'drop your weapon'."

Lancashire Police apologised to Farmer for the "traumatic experience" but confirmed last night that the officer who fired the Taser has not been suspended and remains on duty.

Chief superintendent Stuart Williams, from Lancashire Police, said: "We received a number of reports that a man was walking through Chorley with a Samurai sword and patrols were sent to look for him.

"One of the officers believed he had located the offender. Despite asking the man to stop, he failed to do so and the officer discharged his Taser.

"It then became apparent this man was not the person we were looking for and officers attended to him straight away.

"He was taken to Chorley Hospital by officers who stayed while he was checked over by medics. They then took him to meet his friends in Chorley at his request.

"Lancashire Constabulary deeply regrets what has happened. We have clearly put this man through a traumatic experience and we are extremely sorry.

"We have launched an urgent investigation to understand what lessons can be learned and the matter has been referred to the IPCC."

Farmer says he is taking legal action against the force and wants the officer involved charged with assault.

A 27-year-old man carrying a samurai sword was later arrested on suspicion of being drunk and disorderly.

-A correction was made to the standfirst on 18 October 2012. "IPPC" was changed to "IPCC".