A builder fell 13 metres after a roof collapsed in a new section of Watford FC's stadium.

Emergency services closed Vicarage Road on Tuesday night while firefighters rescued the man, who was trapped in the wreckage.

Fire crews carried him through the building site and onto the pitch where an air ambulance had landed. The man, who has not been named, was taken to Royal London Hospital in Whitechapel with serious leg and head injuries.

The North East Corner of the stadium is currently being redeveloped by construction company, ECS Groundwork Ltd, to include a new club shop and hospitality suites.

Martin Reynolds, owner of ECS, said: "The preliminary investigation has put it down to component failure.

"I can't go any further than that."

Union bosses say it is “disturbing” that work is continuing at Vicarage Road after part of the structure collapsed.

Mr Reynolds admitted workers had been onsite in the days after the roof caved in, but not at the scene of the accident.

The Health and Safety Executive said it was making initial enquiries into what caused the structure to collapse.

Nigel Evans, of nearby Oxford Street, told the Observer: “I heard a shout and then a crash.

“It sounded like ‘woah’ and I could hear the crane moving, so I presumed they had knocked into something.”

Michelle Loghin, 39, and her eight-year-old son Iulian heard a “loud bang” from their home in Aynho Street.

“They were trying to make a platform”, Iulian said.

“It wasn’t strong enough when they were trying to pour concrete in and it fell down. There was a very loud noise and I thought there had been an explosion.”

Cliff Webb, watch commander from Watford Fire Station, said: “We were called to a trapped person. He had fallen from height.

“He was in a difficult position to get to. We made sure it was safe for the paramedics and then we tried to get some spine boards through as quickly as possible.

“He was conscious and breathing and had head and leg injuries and a possible pelvic fracture.”

Watford FC spokesman, Richard Walker: “There was an unfortunate accident involving a contractor’s worker.

“That part of the site has been sectioned off. Builders have been onsite.”

Barckley Sumner, spokesman for The Union of Construction, Allied Trades and Technicians (UCATT), said: “It is disturbing to read reports that workers had returned to work after such a serious accident.

“Following such a serious accident work should not restart until the circumstances of the accident are fully understood and rectified.”

The Health and Safety Executive confirmed it had not stopped work on the site.

Spokeswoman Jill Inglish said: “We’re making initial inquiries, but a full investigation has not been launched yet.”

Mr Reynolds said his builders had remained at the site of the North East Corner where a new club shop and hospitality suites are being built.

He said: “We have not told the workers to not go in.

“We take what has happened very seriously and we have got to reconstruct all the things we believe could lead to a recurrence.”

Cardinal Ltd, which started work on the front of the shop on Monday, have been told by Watford FC not to return until the Health and Safety Executive had finished its investigation.

Cardinal operations manager, Eddie Suchomski, said: “We only started working there on Monday and work directly for the club.

“We’ve been told not to return to work until the HSE have finished their investigations – we’ve been asked to stand down from it all until we get the go ahead to back in.”