The rules apply to the use of auto-diallers in call centres, which can sometimes generate silent calls by dialling more numbers than can be answered by staff.

Previously, an automated message had to kick in two seconds after a homeowner picked up the phone however the communications regulator has now amended its rules so that the two seconds can begin after the person answering the phone starts speaking.

Ofcom said: “The reason for this is that it will make it easier for diallers to detect when a call is being answered by a real person or an answering machine.”

Auto-diallers are more commonly used for telemarketing activities, but they are also used in large-scale telephone survey recruitment. Click here to view the Market Research Society’s regulations for using auto-diallers in research.

The rules state that the number of silent calls generated by a call centre must not exceed more than 3% of the total call volume each day.