Industry regulator Ofcom said it was forced to step in after some companies started charging almost £20 for a 90-second call.

The new cap means the maximum cost a 118 service can charge is £3.65 per 90 seconds, bringing prices back to the levels they were at in 2012.

Jane Rumble, Ofcom’s director of consumer policy, said: “Directory enquiry prices had been rising in recent years, and callers were paying much more than they expected. Our evidence shows this was hurting people, with some struggling to pay their bills.”

While the number of calls to 118 services has been falling by around 40% every year, more than a million people in the UK still use them and many callers are elderly.

Ofcom research found people aged 65 and over are four times more likely to call 118 numbers than those aged 16 to 34 and are far less likely to have internet access when they need to find a number.

Nearly two-thirds of callers to these services said they don’t know how much the calls cost.