A businessman has been arrested on suspicion of attempted murder after confronting a gang who were allegedly attacking his stepson in the family's front garden.

A teenager was left with stab wounds after Colin Philpott, 58, a company director, went to help his 25-year-old stepson, Alex Lee, drive off teenagers said to have been vandalising his van.

After being released on bail following 18 hours in the cells, Philpott described how he awoke last Friday night on hearing noises in the front garden of his detached home in Crowthorne, near Wokingham, Berkshire. He went to investigate and found Lee, his wife's son, with a broken nose.

Philpott, who runs a business cleaning escalators, said: "My stepson was alerted to some youths outside, vandalising one of my vehicles. He … asked them to stop and was attacked … when I appeared on the scene I was set upon as well, and as a result of that one of the youths received some stab injuries, which he had to get medical treatment for. I asked my wife to call the police and ambulance, which she did."

Philpott was arrested on suspicion of attempted murder and later released on police bail until 25 September.

A 16-year-old, who was arrested on suspicion of criminal damage and assault, was taken to the Royal Berkshire hospital, where his injuries were described as not life threatening. Three 17-year-olds and another 16-year-old were arrested on the same charge, and all were released on bail.

Philpott's wife, Susanne, 51, a training consultant, said her husband had rushed out to defend her son with a letter-opener. "My son and I came out at about 11pm after hearing a bang and we saw two young guys outside our house. They returned 15 minutes later – with three others – and all were visibly drunk. I took a digital camera and told them that if they vandalised anything else I'd take pictures as evidence.

"One said that he would kill me and burn down my house. I was terrified and when Alex tried to calm him down, the other four got worked up and attacked him. Alex ended up on the ground with all five of them on him, kicking him in the head and stomach. I was so frightened for him I screamed for Colin, who was in bed.

"He came running out – still barefoot and half asleep – and saw the mess Alex was in so ran back into the house. He grabbed the first thing he saw, which was a letter-opener, and confronted the boys. They attacked Colin and I saw one stumble into the road as Colin screamed for me to call the police."

She said that when the police arrived they arrested her husband. "It was heartbreaking to see him handcuffed and carted off … he is a hardworking, honest, family man and was only trying to protect us."

She added that the neighbourhood had been blighted by teenagers attacking cars and gardens for several months. Other residents said gangs of youngsters had ripped up flower beds, thrown eggs at them and thrown objects through open windows. Neighbours had reported anti-social behaviour to the local council and a councillor is said to have asked Thames Valley police to take action.