An amateur video caught the helicopter in flight

The fault occurred because paperwork explaining a particular repair procedure was in Aberdeen - while the mechanics were working in Cardiff.

The helicopter's owners acknowledged it was a miracle no-one was killed but they said new maintenance procedures will ensure the accident cannot be repeated.

The helicopter crashed into the home of the Patterson family near the busy Coryton M4 interchange on Good Friday last year.

Jointly operated by South Wales and Gwent Police the machine had been following a stolen car in the area of the M4.

The AAIB report praised the pilot Grant Lawrence for his skill in handling the force landing of the machine which had prevented any injuries.

Colin Patterson: Unable to return to work

The South and East Wales Police Air Support Unit leased the aircraft from Veritair.

Tony Jones, a director of the company, said: "The paperwork was completed, but they didn't have it to hand at the time so weren't able to follow the full instructions."

"Engineers not having the right paperwork is not acceptable."

"But we have taken steps with our new maintenance organisation under new Veritair to make sure it is not going to happen again," he said.

Mr Francis said no criminal proceedings had been launched against Veritair or the maintenance company at the time of the crash, Scotia Helicopter Services.

The crash destroyed the top floor of the maisonette home of Colin and Diane Patterson who were watching television with two of their sons.

"We are very lucky. I cannot believe none of us was injured. It's a miracle," said Mrs Patterson,

Their home took more than six months to repair.

Mr Patterson, who is 59, has been unable to return to work as an insurance broker and is suffering from post traumatic stress syndrome.

He said the matter of a legal claim was "in the hands of our solicitors".