A LENGTHY inquest into the death of a North-East airman in secret nerve gas tests 51 years ago is nearly finished.

Ronald Maddison died aged 20 after being exposed to sarin in 1953 at Porton Down, on Salisbury Plain, Wiltshire.

Leading Aircraftsman Maddison, from County Durham, collapsed within minutes of having 200mg of sarin drops put on to his arm in a chamber at the top secret base.

The original inquest was held behind closed doors "for reasons of national security", a decision made at the highest levels of government in the 1950s.

The inquest was reopened after years of campaigning against its open verdict - and lawyers say the outcome of the inquest could lead to legal action by the veterans of Porton Down, who claimed they were duped into taking part in similar dangerous trials.

Summing up the case, Wiltshire Coroner David Masters told the jury that it must reach a verdict of either death by unlawful killing, death by misadventure or return an open verdict.

He said: "Your task will be to consider all the relevant facts and figures.

"You must ask yourself if Ronald Maddison consented to the application of a chemical warfare nerve agent in a non-therapeutic experiment.

"If he did not give his consent, then a verdict of unlawful killing remains open to you."

He told the jurors that they could reach a verdict of death by misadventure if they found that the experiment had unexpectedly gone wrong.

He said: "A verdict of misadventure occurs if it is probable that the cause of death arose from some deliberate and lawful human act which has unexpectedly and unintentionally taken a turn that leads to death."

Mr Masters told the Trowbridge hearing that an open verdict could be reached if the evidence did not disclose the means whereby the cause of death arose.

He said the political, military and socio-cultural climate at the time of the tests must be examined. The jury must assess what Mr Maddison knew about the experiments carried out upon him.

Reminding the jury of evidence heard earlier in the inquest, Mr Masters said the sarin experiments were conducted to find out what dose would cause incapacity or death to humans.

The court heard that many soldiers had undergone the tests at Porton Down in which sarin was dropped either on their skin or on cloth.

The summing up is expected to last for five days.