Vodafone has avoided a heavy fine by the UK telecoms regulator after expanding its 3G network to meet coverage obligations.

In November 2013, the regulator reported that the mobile operators EE, Three and O2 had all met their 90% 3G coverage obligations, but Vodafone failed to meet the obligation, reaching 88.66%.

The company was offered an extended deadline until the end of 2013 to reach the 90% mark, which it managed to meet ahead of the deadline.

The regulator said it takes the requirements of its licensees very seriously, and breaches of these obligations can incur a penalty.

"In this case, once informed by Ofcom, Vodafone provided a plan to address the shortfall. This involved work to upgrade 129 mobile transmitter sites, which was completed on time," the regulator said.

"Having taken these factors into account, and the margin by which the target was missed, Ofcom has decided that it will not take any further action on this occasion."

The regulator said it will carry out research into the quality of mobile reception and coverage, such as information on the proportion of ‘dropped’ calls that consumers experience.

Ofcom will also publish new data revealing 3G and 4G mobile broadband performance in the spring.

Ofcom has placed a coverage obligation on a licence acquired by O2, which requires the company to extend indoor 4G coverage to 98% of the UK population by 2017 at the latest.