Ofcom has ruled that businesses using automatic dialling machines to make cold calls to several homes at once can wait until the person answering finishes speaking before counting down a two second limit on the time it takes a handler to pick up the call.
Previously companies needed to respond to an answered phone within two seconds. Call centre staff found that in this time they were sometimes unable to determine whether the call had been picked up by a person or an answerphone.
Rules also stipulate that abandoned calls must not account for more than 3% of all calls made in the space of 24 hours.
Campaigners against telemarketing have called the decision a loosening of the rules.
According to research 3 billion telemarketing calls are received each year in the UK and consumers receive 1.2bn silent calls a year.