One of the couple's daughters, Danielle, is understood to have frantically raised the alarm as the gunman fled.

A 23-year-old man was arrested in the early hours of Sunday morning at an address in Newbridge, near Penzance, in a major operation involving armed police.

He was taken to hospital for treatment to facial injuries, which are understood to be self-inflicted.

A family spokesman said yesterday they were all shocked by "these terrible and very unexpected events".

Porth Kea House, where the couple lived, was cordoned off yesterday while forensic teams carried out a detailed examination of the scene.

Scenes of crime officers are due to continue the hunt for evidence at the house today and door-to-door inquiries will also be carried out.

The daughter, Danielle, who is thought to be in her late teens, is being comforted by relatives and will be helping the police as a key witness.

A police spokesman said: "Police received a 999 call from the address at about 9.50pm. Officers attended and found two casualties and both were taken to hospital. Unfortunately, a 41-year-old man later died.

"Following inquiries, at 5am on Sunday, officers went to an address outside Penzance and arrested a 23-year-old man without incident."

A firearm has been recovered and is being examined by experts. No further details about the gun have been made public.

Relatives were yesterday at the bedside of Mrs Hustler, who has been transferred to Derriford Hospital in Plymouth. Her current condition is not known.

The family-run firm Clear-Flow is based at Bissoe, near Truro, and is the county's largest waste pumping and liquid haulage firm.

It has contracts with companies like South West Water as well as dealing with domestic septic tanks and drain clearance.

The family are Jehovah's Witnesses.

Tim Mears, a friend and fellow Jehovah's Witness, was asked by the family to express their shock at what had happened.

He said: "Friends and family are providing loving support and comforting those affected. Our thoughts and prayers are with Amanda and her two daughters at this most difficult time.

"Adam Hustler was a loving husband and father. He was a generous and caring person who thought the world of his wife and daughters.

"He was thoughtful and always ready to help and support others when they needed help. He is a great loss to all who new him, and especially those that shared his Christian values."

Shocked villagers in Porth Kea described the family as "lovely" and "quiet".

Neighbour Tony Blight said he had spoken to the couple on Saturday and everything had been "fine".

He added: "We've known them for as long as they've been in the village – five years or so – and they're a lovely family.

"Adam's a very quiet man and he wouldn't hurt a fly. He and Amanda are very hardworking people. They enjoy family life.

"I popped in to see them on Saturday and everything was fine. It's a real shock."

The country road up to the family's large, detached home was cordoned off while the investigation continued yesterday.

Another neighbour, Les Boulter, 61, who has lived in the hamlet for more than 20 years, said he was shocked.

"There was a fireworks display going off last night so I didn't hear anything. It would have certainly masked any gunshots.

"The first I knew was when my daughter came back late and said the road had been blocked off by police.

"It's the biggest house in the village and the most expensive – it was three-quarters of a million when they moved in about six years ago and they've extended it since then.

"They are quiet people and keep themselves to themselves.

"It's very sad that something like this has happened."

Mr Boulter said he had dealt with Mr Hustler's company in his capacity as an electrical engineer.

"The company was expanding and I know Adam was well thought of. They are a close-knit family. This sort of thing doesn't happen in Porth Kea."

Another neighbour, who did not want to be named, said: "Nothing ever happens here. It's a big shock to hear that someone's been shot so close by.."

Porth Kea is a hamlet of fewer than 20 houses, close to the banks of the River Fal, in an area of outstanding natural beauty.

The single road through the hamlet was sealed off by police as inquiries into the incident continued.