The “It's your Call” hotline, launched by the TUC as part of its campaign on call centre conditions, has received 400 calls in its first week.

Callers have complained about bullying, impossible sales targets, late payment of wages and hostility to unions.

Calls to the line have so far included reports of a centre where staff have to physically attend the office to report in sick, and another where permission has to be sought to go to the toilet and the visit is timed.

The calls have come from all over the UK, but nearly a third have come from South Wales and Scotland, favourite locations for call centres.

Last week, more than 80 current or former staff said they were suing BT for damage to their hearing, balance and quality of life from the condition known as acoustic shock.