The UK Department of Health has on Sunday (2 April) announced an urgent investigation into allegations that suicidal people calling the NHS 111 helpline to seek advice are kept on hold until they hang up because the staff on duty are either asleep or playing cards.

The alleged practices were highlighted in a report published by The Sun, which carried out an undercover investigation that also found the toilets at the call centre had traces of cocaine.

The Sun placed an undercover reporter at the NHS 111 call centre office at St Charles Hospital in Ladbroke Grove, west London following a tip-off from a whistle-blower.

The helpline provides 24-hour support to distressed callers who are on the verge of committing suicide. It caters to callers from 11 boroughs in north, west and central London.

However, the Sun reporter found untrained staffers were made to handle the calls when the managers were busy playing cards or taking a nap at their desks during night shifts.

When struggling to use the computer systems, the trainers allegedly asked workers to take the calls and lie to the callers that they were experiencing a technical glitch.

The callers were also put on hold to prompt them to finally disconnect the call despite training manual guidelines clearly stating that callers should never be put on hold if deemed unstable or suicidal.

The Sun reporter narrated an instance when two handlers repeatedly "muted" a suicidal woman before she eventually hung up. Later, one person said: "She's disconnected, and may be dead." Another worker said that suicidal callers are "a bit needy and want to talk".

"What can you say to them? They make it seem in training like you should be like, 'So what's your favourite colour'?" one handler reportedly said, defending their actions. The undercover reporter also narrated an incident when one handler hung up on at least three patients, including one with heart palpitations.

The call centre is run by private firm London Central and West Unscheduled Care Collaborative.

Dr Simon Douglass, the firm's medical director, said that they take allegations extremely seriously, and said they have launched an urgent investigation. "All issues relating to staff conduct are extremely important to us, particularly in relation to patient safety."

Terming the claims as "clearly completely unacceptable" if found to be true, a health department spokesman said: "The NHS is now urgently investigating and if any wrongdoing whatsoever is found, including criminal actions, we will want to see the police and relevant NHS regulators alerted as necessary."

Condemning the alleged practices at the call centre, former health minister Norman Lamb MP said: "We are talking about life and death situations and people who are desperate and who have chosen to seek help. To let them down in that way is horrifying."

Sophie Corlett, of mental health charity Mind, said: "It should be a basic requirement of all NHS 111 services that staff are well trained and offer a human and caring response to people in need. We lose 6,000 people a year to suicide."