It is a sunny Saturday afternoon in Covent Garden and we are all learning how to kill ourselves. The venue is a nondescript community centre in Stukeley Street. It usually hosts activities for children, so there are crayon drawings and anti-bullying posters on the noticeboard. Today, however, a purple pop-up banner displays the Exit International logo and its mission statement: ‘A peaceful death is everybody’s right.’

Admittance to the four-hour workshop costs £50 and is reserved for those over the age of 50 and the seriously ill. The company collects around the tea hatch, everyone fanning themselves with their copies of the Exit International magazine, Deliverance.

There are 80 or so men and women, grey-haired and crepe-soled. They arrive on each other’s arms and with walking aids. A mobility scooter does a three-point turn in the narrow corridor. Philip Nitschke sits at the front with a laptop and a screen, ready to embark upon his specialist topics — hypoxic death, poisons, barbiturates, the legal issues and the ‘Swiss options’.

He is Australian, personable, jokey and voluble. He wears quite loud shirts, spectacles large enough to be amusing, and he has been photographed looking introspective in a field full of pink tulips. He doesn’t need a microphone and he warns those who want to ask questions not to wait for him to draw breath because he doesn’t draw breath.

Now 69, he has been committed to the right-to-die movement since 1996. His activities in Australia’s Northern Territory earned him the press nickname Dr Death when, having built a computer hooked up to administer a lethal dose of barbiturates, he assisted in the deaths of four terminally ill Australians.

Since then he has travelled the world advocating the human right to a pain-free death, which he believes should be at the time of a person’s choosing. He shows us a photograph of the French academic Lisette Nigot, who was healthy but did not wish to live beyond the age of 80. ‘I ’av ’ad enerf,’ she told him, and left a note thanking him for his support when she took a fatal overdose in 2002. He is a qualified doctor. He graduated from the University of Sydney Medical School in 1989 and has worked as a GP. He retired from formal medicine in 1997 to found what is now Exit International.

The law is different around the world. In Holland, where Nitschke now lives, a life can be deliberately ended by a healthcare professional. Here, in England, assisted death is still illegal and carries the threat of a long prison sentence. ‘You are in the dark ages,’ he says.

The consequence has been the development of a network of underground dissent where emails have to be encrypted, payments are by bitcoin, and there are stories about old people being hassled by the police .

In 2006 Nitschke and his colleague Fiona Stewart, an academic sociologist, published the first version of the Peaceful Pill Handbook. A manual and a manifesto, it is now available online, where it is regularly updated to include the latest information about cyanide, morphine, and the correct way to control the gas flow of a helium cylinder. He warns us against the benzodiazepines; valium won’t kill you, he insists. You could take a ‘bucket full’ and still not die.

He shows us the film Doing It With Betty, in which an elderly former nurse demonstrates how to make a suicide hood for inert gas asphyxiation using a plastic bag and a drawstring in much the same manner that a member of the Women’s Institute might present a talk on the best way to make marmalade. Betty acknowledges that you might not look your best at the end of this intervention. ‘You might like to get your hair done,’ she suggests.

We break for a cup of tea and return to discuss the drug of choice for those seeking painless deliverance. Nembutal is a barbiturate which has been used on Death Row and by the medics at Dignitas, as well as by vets to euthanise dogs. In liquid form, it is available over the counter in Mexico and other countries. Bought in pet shops, its boxes carry a picture of a golden retriever. One bottle will be enough, Nitschke tells us, though most people buy two and store them in the fridge, where they can last for about 30 years.

A rise in the online demand for Nembutal has created an unpleasant subculture of fake websites and dodgy drugs, while the Chinese have developed a powder form whose content is difficult to check without a lab test.

Nitschke tells us about the Exit International Research and Development Programme, whose ‘practical solutions’ are to be presented at a conference in Canada later this year. Topics will include ‘But is he dead yet? An app that lets you know by SMS’, ‘Drones: Do They Have a Role?’, ‘Designer Drugs (the neo-barbiturates)’, ‘Hydrogen Sulphide: Misunderstood and Underused’. And how to use the CS10 IR Spectrometer to test Nembutal quality.

The new technologies of self-deliverance are pioneered by Nitschke and informed by his own opinion that, while most people recognise the right of an individual to take their own life, nobody wants to be an executioner. Autonomy must be integral to the design.

‘Roight,’ he says after a long Q&A about anti-emetics. ‘Let’s git on to the guesses.’

Up comes a slide showing a nitrogen gas cylinder sold through his sideline Max Dog Brewing. He says nitrogen is a gas we can trust; it offers a peaceful death, quick and undetectable. So he supplies it as a £900 home kit that arrives with a built-in pressure gauge and flow-control mechanism. ‘You never need to go to Switzerland,’ he tells us.

The woman next to me is 72; she has been watching Prunella Scales in Great Canal Journeys on television and is worried about dementia, which she points out ‘can last a very long time’. She has been a member of Exit for three years but this is the first workshop she has attended. She doesn’t want to kill herself immediately, but thinks it is a good idea to have ‘something in the store cupboard’.

As we make our way back to the street, the future of civil liberties lingers as a slide on the wall. The SARCO Nitrogen System is Philip Nitschke’s latest invention. A human- sized metallic capsule which can double up as a coffin, the pod allows the patient to self-administer a deadly dose of nitrogen. The plan is to develop the equipment for use with 3D printing technology, so you can have your death flatpacked and delivered to your door. All you have to do is get in, push a button and you’re gone. It’s brilliant really.