Talk Talk’s call centres are dealing with more than 20,000 calls a day, and it cannot train new staff fast enough.

Charles Dunstone, Carphone’s chief executive, has admitted Talk Talk is struggling to keep up — even with more than 1,000 people working in the call centres.

He wrote on his blog, or internet diary: “To my immense frustration even this huge increase in our capacity is still insufficient to keep up with interest ... there are still queues to get through at most times of the day.”

The number of broadband customers that Talk Talk has attracted will be one of the main points of interest in its full-year results. Although the broadband offer was only launched in April, some analysts believe Talk Talk has already signed up about 150,000 customers, and is adding 20,000 more every week.

This is about the same number as Bulldog, the Cable & Wireless broadband subsidiary that has only recently overcome two years of severe customer-service problems.

Carphone is investing more than £100m in broadband, including start-up losses, in its bid to challenge BT. The “free” offer requires customers to pay £11 a month for line rental and sign up for Talk Talk’s landline service for £9.99 a month.

The City expects Carphone to report pre-tax profits of about £135m, a third higher than the previous year.

Orange, the mobile-phone company, launched its own “free” broadband offer last week, although it is available only to contract customers who spend at least £30 a month. The move is part of the company’s drive to offer “converged” fixed-line and mobile services.

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