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 answering machine.
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 Ofcom, 3bn telemarketing calls are received each year in the UK. Consumers receive 1.2bn silent calls a year.