Fellow ex-Wipro employee Mr Kharbanda recalls: "You are trying to remember what the other guy said and you are listening to [the next] fellow. . . and you mix it all up. That is when you mess it up."

Mr Sameer says poor performers were sometimes hauled up in front of their colleagues for ridicule and alleges a meeting with two managers descended almost into a brawl, with him being physically manhandled.

Meanwhile, on the call floor, colleagues were downing tools. According to Rohit Kharbanda, Mr Sameer's treatment was being met with such shock and anger that staff spontaneously grilled their managers for nearly half an hour - as the number of calls waiting soared. Mr Kharbanda says: "We all put our phones on hold. Everybody was concerned."

This was a crucial moment. According to Mr Kharbanda, an agent could be hauled up for allowing the phone to ring seven times. He says failing to take or "dropping" a call is considered an act against the "integrity of Wipro" - a major offence. Again we asked Wipro if this was the case but it refused to comment.

Work eventually restarted and Mr Sameer was soon on his way home. He never worked at Wipro again - following a six-week suspension he was "terminated" in September. He claims other members of the team were transferred hundreds of miles away.

No one knows how common this kind of experience is. There are undoubtedly tens of thousands of contented Indian call centre workers - and no evidence that these allegations are representative of Wipro as a whole. But Dave Fleming, a national officer at Amicus, Britain's largest private sector union, says cases like Mr Sameer's underline the need for effective unions to support Indian offshore workers.

He says: "When these companies go offshore they say they replicate the work experience of the home country in India. But if that is the case then working rights and trade union representation should also be replicated. At the moment that is not happening."

But last year, finance union Unifi - now part of Amicus - promoted union representation for offshore workers in a series of agreements regulating offshore plans of UK banks.

And through its international links with unions affected by offshoring, service union federation UNI is organising a trade union for offshore call centre workers. Centre For BPO Professionals (CBPOP) director JSR Prasad says a central demand is for companies to "sit up and listen" to criticisms.

Meanwhile in Mumbai, the Young Professionals Collective is set to tackle everything from the racism and phone rage of some overseas customers to the problems of working permanent night shifts. And in Delhi, human rights NGO Kartavya is taking call centre cases to the Indian labour commissioner.

Mr Sameer says: "I would like to see [Wipro president] Azim Premji spend two days non-stop taking calls and handle all the needs of customers and not complain. And by the time he finishes he will be ready to resign. I am sure he cannot handle the job I did every day."

"I used to encourage people to join Wipro. I said ''it's good pay, you know. It's a little difficult but good pay''. But now I say ''if you really don''t like yourself then do the call centre job''."