Pawan Kumar, who learned his trade from his father and grandfather, is paid £30 a month as a registered executioner

The phone call will come some time in the next few weeks, and when it does Pawan Kumar will be ready.

"I have already done a test run, with a sack of sand the weight of the criminal. I have been waiting for this moment all my life," said the part-time clothes hawker in the northern Indian town of Meerut.

For while selling shirts from the back of a bicycle pays Kumar's rent, his vocation lies elsewhere: the 52-year-old is one of a handful of officially registered professional hangmen in India.

So far, however, he has never actually carried out an execution.

Last month, he was called to a jail in the city of Jaipur, 250 miles south of Meerut, to execute a condemned prisoner. At the last minute though, the man was reprieved.

In early September, Kumar was scheduled to hang Surinder Koli, one of India's most notorious murderers. But another last-minute decision meant the execution was postponed to allow further legal argument, though just until the end of next month.

"I wouldn't say I was disappointed. That would be a personal thing. I am just sorry that a man who has committed such heinous acts has not died yet," said Kumar.

In India, the death sentence is reserved for cases that are deemed "the rarest of the rare". In the past decade, there have been only three executions. The 350 convicted prisoners who theoretically face hanging include four men found guilty of the gang rape and murder of a 23-year-old student in Delhi in 2012.

Even though they are rarely called on to carry out an execution, hangmen are paid a monthly stipend by local state governments of about 3,000 rupees or £30. Even so, prison administrators in this country of 1.2 billion struggle to find executioners.

At one stage, the north-eastern state of Assam was forced to issue a nationwide appeal for a hangman. "It is not surprising there are so few. It is a hard thing for a person just to kill an ant, let alone another human being," said Kumar, who supports a family of seven.

Following a centuries-old practice on the subcontinent, the post of executioner is inherited. Kumar's grandfather carried out about 60 hangings in his 40-year career, including one of the assassins of prime minister Indira Gandhi, who was shot by her bodyguards in 1984.

Kumar's father, who inherited the post in 1989, conducted half a dozen executions. Kumar assisted both men, thereby, he explained, learning the trade's "special techniques".

"They were proud of what they did and I am proud of helping them. It is a duty. Justice is being done. A criminal is being killed and crime is going to come down in India as a result. That's why we feel nothing when we kill a man," he said.

These days the identities of those carrying out politically sensitive executions – such as that of Mohammed Ajmal Kasab, the sole surviving attacker from the 2008 terrorist attacks on the city of Mumbai (executed in November 2012), or Afzal Guru, an alleged Kashmiri militant who was hanged for the 2001 attack on India's parliament in February 2013 – remains secret.

Kumar, however, has become a minor media star, with the prospect of greater celebrity if Surinder Koli, the murderer reprieved last week, exhausts all options to avoid death.

Koli, a 42-year-old domestic help, was arrested in 2005 after human remains were discovered in a drain near a house on the outskirts of Delhi, the capital, where he worked.

He was convicted of five cases of murder, rape and cannabalism and faces another 14 counts.

Kumar believes he will be the last in his family to practise the trade. His eldest son, who is 21, has shown little interest.

"If he wanted to, I would train him. But he's studying banking and has just applied for some post working in the accounts department of Indian railways," said the aspirant hangman. "I think his interests lie elsewhere."