Builders working on the New Barnet site where an unexploded Second World War artillery shell was found last week claim they were unfazed by the discovery.

The device was spotted by a digger driver, who unearthed the 20 pound round of live ammunition in soil that had not been touched since the 1940s.

Bomb disposal experts were called to the site of the JCoSS school development, in Westbrook Crescent last Wednesday, and workers were evacuated at about 4pm.

The adjoining East Barnet Upper School was also cleared of pupils before a controlled explosion was carried out.

The site manager from the building firm Ardmore, who didn't want to be named, said if the shell had been another foot underground, it would never have been found.

“Throughout 40 years of digging I’ve not found so much as damp squib,” he said.

“It didn’t faze us, there was no real panic; although it seemed the police got a bigger fright.

“We had a bit of a laugh and a giggle, but the kids seemed to have more excitement with their alarm going off.”

The police cordon was removed at about 6pm and workers were able to return the following day.

The manager said: “We were more worried that we would have to stop the whole job and do a risk assessment. It’s a tight programme and the last thing we would want to do is shut the job down.”

He said a full independent survey had been made by bomb experts, who evaluated the site to be low risk, which means the chances of other live shells being in the ground is unlikely.

Michael Phillips, the Chair of the JCoSS Trust, which is responsible for the building project, said “These types of incidents are not uncommon during major construction projects so there are clear and established procedures for dealing with them.

“Safety is our top priority so the site and surrounding areas were quickly cleared to enable the bomb squad to do their job.”