Most of the increase came from a surprise surge in local calls, which went up by almost 20 per cent, from 33 million to 39.3 million. Long-distance calls connected rose by 0.9 million to 13.9 million, as did international calls, which edged up from 1.18 million to 1.23 million.
BT had no explanation for the scale of the increase in local calls, which were not included in this year's seasonal discount offer. It gave customers three minutes on the phone for the price of two minutes, but applied only to trunk calls made within the UK.
One theory could be that customers had wrongly assumed the promotion applied to all phone calls, while another suggestion was that rising consumer confidence had encouraged a general increase in phone use.
Figures on the length of calls will not emerge for several days, though a BT spokesman said each Christmas Day call usually lasted an average of 12 minutes, whereas the total time spent on the phone by residential customers during an ordinary day was nine minutes.
He explained: "It always works out when the final figures are calculated including the number of calls and call lengths that Christmas Day is one of the busiest days of the year for us. This is because calls tend to be much longer than average calls on a normal day, for obvious reasons."
Figures from Mercury released yesterday also showed a Christmas boost, with total calls made by the company's customers rising from 2.8 million to 3.02 million. Of these, 1.12 million were international, compared with 800,000 international calls in 1995. Mercury's Christmas Day promotion cut the cost of national calls to a penny a minute.