David Edmonds, director general of the industry regulator Oftel, is concerned that they will not be able to cope with connecting the anticipated large number of new phones to the networks.

What most of the UK wants for Christimas

It follows the long delays in getting connected seen last Christmas and in August this year following a rush sparked by a supermarket price war.

Mr Edmonds said: "I want to know how they have estimated demand for registrations and credit top-ups during the Christmas period and what they will do to ensure customers will not experience problems."

He said forecasts are for more than 3.5 million pre-pay phones to be sold between now and Christmas, more than double the record sales achieved in the same period last year.

Numbers have doubled

That figure equates to 63,000 phones sold each day - or roughly one every two seconds between the end of October and 25 December.

Mr Edmonds said that last year pre-pay phones were the Christmas present.

He added: "This year it is predicted that in excess of 3.5 million pre-pay phones will be sold ... more than double the record sales achieved in the same period last year."

Mr Edmonds said the service for switching on pre-pay mobile phones to the networks had been far from satisfactory in the past when companies had been unable to cope with demand at peak times.

Thousands of customers were unable to use their Christmas present for weeks last year while in August, following a supermarket price war on pre-pay phones, companies once again failed to meet demand.

Pre-pay boom

Oftel received more than 600 complaints in August alone as customers found phone helplines jammed.

There has been an explosion in the ownership of mobile phones in the UK in the past two years.

The rate of sales has risen dramatically since the launch of pre-pay phones.

Customers put off by the complicated array of different tariff packages available have warmed to the simplicity of the pre-pay system.

It involves customers paying to buy a handset and then buying airtime 'vouchers' as they go.

By September this year there were 19.5 million mobile phones in circulation in the UK with an estimated 1.8 million of these on pre-pay packages.