BT chief executive Sir Peter Bonfield is expected to leave next summer once the telco has finished its slash and burn debt-reduction programme.

Although Bonfield has a contract until December 2002, it is thought he will leave next summer after overseeing the break-up of Concert, BT's joint venture with AT&T - details of which BT is expected to announce next week, according to a report in the Financial Times.

After pursuing what now looks like over-ambitious expansion, Bonfield was retained by BT chairman Sir Christopher Bland to help implement BT's debt-reduction strategy.

This has seen a new rights issue, asset sales, job cuts, sales of overseas interests and its directories unit Yell, with the £7bn O2 demerger and the breaking up of loss-maker Concert still to come.

In April, BT was £27bn in debt and in danger of being given a poor credit rating.

Earlier this week, possible Bonfield successor Pierre Danon, the chirpy chief executive of BT Retail, told reporters that previously mooted further restructuring measures were no longer on the agenda.

Meanwhile, BT shares fell almost 10 per cent on Thursday to 340p after investors were nonplussed by O2's poor growth among mobile subscribers in the UK and Germany.

O2's UK mobile operator, BT Cellnet, increased its subscriber base by 78,000 in the last quarter, well below the take-up figures of its rivals.

Vodafone and Orange added 251,000 customers (to 12.5 million) and 320,000 (12.2 million) respectively over the same three-month period.

Even Virgin managed 172,089 new customers, taking its total to 1,181,333.

O2's Cellnet, meanwhile, is lagging in third place with less than 11 million subscribers.