National Grid Gas (NGG) and Northern Gas Networks (NGN) have been fined by the regulator Ofgem for not attending to gas leaks in time.
NGG has been fined £4.3m, while NGN has been fined £900,000.
Gas distribution network operators have to respond to 97% of uncontrolled gas escapes within one hour and 97% of controlled escapes within two hours.
A controlled escape is one that may be controlled by the person reporting the leak using advice given over the phone.
An example of a controlled leak would be one in which a householder was able to switch off the gas supply to their home at the meter.
The fines cover the period from April 2010 to the end of March 2011.
“Ofgem accepts that many parts of Britain experienced bad weather conditions over the last year and individual members of staff from NGN and NGG worked hard in difficult conditions to reach customers that reported gas escapes,” said Rachel Fletcher from Ofgem.
“However, both companies need to plan better for bad weather and ensure that adequate resources and contingency plans are in place to meet the annual targets.”
National Grid accepted the fine and said: “We take our responsibility to attend and manage gas escapes very seriously, and we have learned lessons from last year that we have embedded into the improved plans we have put in place for this coming winter.”
Mark Horsley, chief executive of Northern Gas Networks, said: “We have worked closely with Ofgem throughout its investigation and demonstrated that we have learnt from last year’s winter experience.”
“Winter 2010/11 severely tested our network and we would like to apologise to anyone who was adversely affected, but also take this opportunity to reassure our customers that we have taken action.”
Ofgem said the fines would have been bigger if both companies had not co-operated with the investigation and taken steps to improve the situation for the coming winter.