An amateur photographer who caused a decommissioned nuclear power station to be put on lockdown after he breached security was jailed for six months on Thursday.

Convicted robber Nicolas Bates, aged 29, of Coventry, had jumped over a 6ft high safety fence at Trawsfynydd in Snowdonia which shut down in 1991, a district judge was told at Caernarfon court.

Bates pleaded guilty to trespassing on a protected site on March 16, possessing a lock knife, having cannabis, and having a hunting knife in his car.

Diane Williams, prosecuting, said Bates had been spotted by a contractor who noticed he wasn’t wearing a hard hat and hi-vis clothing in a restricted area. She said :”100 staff at the site had to be on lockdown that day because of the breach of security.”

The prosecutor said Bates was escorted from a reactor roof and he said: "I was just taking pictures.” The defendant said he did research on Wikipedia and he showed a Nikon camera.

Security guards detained him until police arrived. Bates had a lock knife and the second knife was in his car with smoke grenades and other items.

“He said he hadn’t seen the warning signs and he went to the site to take photographs,” Mrs Williams said. He claimed the knives were used to cut wires when entering derelict sites. Bates had driven from the Midlands.

“It seems the defendant has on his Facebook page, or some form of social media, posted photographs of a similar nature,” the prosecutor added.

Sion Hughes, defending, said the lock knife was for camping and there was no suggestion it had been used to threaten anyone. Bates’s hobby of taking photographs had landed him in a serious position. Neither knife had been brandished, the lawyer stressed.

A probation officer said Bates had been 20 minutes into taking snaps when he saw a worker and went on the roof. He was a personal trainer with mental health issues.

District judge Gwyn Jones told Bates: "You claimed this was a derelict site and you obtained that information from Wikipedia. However, basic commonsense and a very elementary knowledge of physics suggests nuclear sites are dangerous places and there is still a potential risk of harm from radiation.”

Judge Jones said such sites were covered by strict security and having scaled a fence Bates made his way to a sensitive area. “As a result of your actions you caused there to be a lockdown for those 100 or so members of staff,” he added.

Bates had no car insurance and was a provisional licence holder. The judge ordered that he be deprived of the photographs of the site which if in the wrong hands “could potentially cause a risk of harm.”

The 26 weeks total sentence included 16 weeks for entering the site.