Three people have admitted possessing the chemical weapon mustard gas at a former Second World War RAF base.
Martyn Tasker, 39, Michaela Tasker, 31, and Stuart Holmes, 50, were arrested in connection with the discovery of containers filled with highly noxious substance in Lincolnshire woodland in October 2017.
Police declared a "major incident" after the canisters were first discovered on the former air force base near Woodhall Spa.
Bomb disposal officers had to be called in and further testing was carried out on the substance at the Government's specialist Porton Down military research laboratory.
At Lincoln Crown Court on Thursday, the trio admitted possession of mustard gas canisters and discharging mustard gas into fresh inland waters, and Holmes also pleaded guilty to depositing mustard gas in a manner likely to cause pollution of the environment or harm to human health.
Martyn and Michaela Tasker were granted unconditional bail and will be sentenced on a date to be fixed.