The head of O2 has apologised to customers who could not make phone calls because the mobile operator’s London network was overwhelmed by bandwidth-hungry smartphones.

Ronan Dunne told the Financial Times he was disappointed with O2’s network performance in London since the summer. But the UK’s largest mobile phone operator was making good progress towards fixing the problems, he said.

O2 ran into significant network difficulties in the capital during the second half of 2009 as customers with smartphones such as Apple’s iPhone ramped up their use of applications that repeatedly pull data off the internet at short intervals.