An environmental protester who scaled the chimney at Didcot power station was convicted of aggravated trespass despite arguing he did so to save lives.

Carl Van Tonder, a 20-year-old student of Wellington Street, Oxford, was one of nine activists who broke into the plant last October and climbed to the top level of the exhaust chimney.

Eleven others chained themselves to a coal conveyor belt during the demonstration, which was planned to last a week but ended after 48 hours.

The 19 other protesters admitted the offence at an earlier hearing, but Van Tonder, was tried in front of a district judge at Oxford Magistrates’ Court today.

Giving evidence,he said the Global Humanitarian Forum estimated that 300,000 people a year were killed worldwide due to climate change.

Claiming that Didcot power station was responsible for producing 100,000 tonnes of carbon dioxide a week, Van Tonder said shutting down the plant for seven days would have saved lives.

He said: “Our intention, and I think we were partially successful in this, was to save between one and two human lives.”

Van Tonder said NASA scientist James Hansen had called power stations “death factories” and had urged people to take direct action against them.

Brian Payne, prosecuting, said: “Mr Van Tonder has put forward far too generalised an assessment of risk because he is unable to point to a person or groups of persons immediately under threat of death or serious injury. While one can see the statistical argument, that’s merely what it is.”

Van Tonder, who admitted committing aggravated trespass but put forward the defence of “necessity”, said: “This place is ten miles from where I live and is the single biggest contributor to climate change as I see it in the county.”

District Judge Tim Pattinson said Van Tonder had argued his case in a “clear, articulate and intelligent manner” but said he had not acted in a “reasonable and proportionate” way.

He said the effect of closing down the power station, leading to a shortage of electricity could have led to “loss of life or serious injury”.

Van Tonder was given an 18-month conditional discharge and told to pay £500 costs.

Outside court, Mr Payne said: “In bringing this successful prosecution, the Crown Prosecution Service is not seeking to hamper or check legitimate protest.

“Protesters who step over the line of acceptable demonstration into criminal offending will be considered for prosecution.”

Van Tonder said he was not surprised by the verdict but said he was pleased to have aired his views in court.

He added: “My personal situation doesn’t change. My views on the court system and activism, and my resolve, are as steely as ever. These are things that really need to be addressed.”