The service is used mainly by businesses, and by elderly people who may not be comfortable using the internet to find the number they want.
But what most people don't realise is that there is a much cheaper alternative - and it's run by the same company, The Number UK.
If you call 118 811, your enquiry will cost just £1 a minute, plus your network provider's access charge. You won't, though, get the number texted to your phone, and you'll only be able to ask for one number at a time.
And if you don't mind an automated service, The Number UK even offers a directory enquiries service that's completely free - just call 0800 118 3733. You'll have to put up with a 20-to-30-second advertisement at the beginning and of the call, but you won't have to pay a penny.
"There isn't any excuse for these firms to charge extortionate fees. They are preying on unsuspecting customers, as who would agree to spend £50 on a short call?" Martyn James, of complaints service Resolver, tells the Mail.
"The fact that you can get the same service for £1 but this information is hidden away should tell everyone what they need to know about how these services work."
Two years ago, regulator Ofcom changed the pricing model for numbers beginning with 118, 084 and 087, ordering companies to make their pricing model clearer.
But earlier this year, it said it still wasn't happy and was carrying out a review.
"Ofcom has been monitoring the costs of the more expensive services, which have risen significantly in recent months as fewer people use these services," it says.
Other providers include Yell on 118 247 and BT on 118 500, with both charging £2.75 per call, plus £2.75 per minute.
Most outrageous bill mistakes
Most outrageous bill mistakes
Carol Sandford, 72, called 118 118 from her mobile phone unaware of the charges involved. Calls to the number cost £1.88 per call and there is also a £2.57 per minute charge from landlines. TalkTalk raises this to £5.68 for the first minute and £3.28 per minute after that. TalkTalk told Carol the charge £81.12 charge was correct but luckily 118 118 were kinder, offering to repay the charge in full. Read the full story here.
One Londoner was more than a little confused when his debit card was declined while he was trying to buy just six bottles of American craft beers. But he quickly realised that instead of the £22.30 he owed, he had been charged £223,000! It's thought he punched in the PIN number before the machine was ready and it added the numbers to the total. Luckily the 28-year-old saw the funny side and laughed the incident off. Read more on the story here.
Early Lewis from Detroit was amazed to find his water bill was almost 100 times as much as he was expecting. The bill claimed that Lewis had used 3,740 gallons of water in just one hour. Thankfully common sense prevailed and the Water and Sewage Department admitted it was a mistake and subsequently charged Lewis the $36 he should have been charged initially. Read more on this story here.
George MacIntosh, 73, was charged a staggering £200 for premium-rate gambling texts he didn't intend to sign up for. Unfortunately this wasn't a scam but a legal service from a company called Zamano. It seems the retired vicar had accidentally signed up after responding to an initial text from the company. Read the full story here.
Philip Groves was amazed to receive a £1,411 bill from Vodafone last year for his 10-year-old daughter Trinity's phone. It turns out Trinity had watched 28 hours of instructional loom band videos on YouTube, assuming her phone was using wifi. But the wifi had cut out, leaving her phone using the data allowance at it's highest rate. Vodafone refused to cancel the bill and threatened legal action. Read more here.
Daniel Pontin was in for quite a shock after opening a gas bill charging him £31,000 for a year's worth of gas in a one-bedroom home. Pontin claimed his meter was broken when he moved in and was initially charged £35 a month for six months before he stopped receiving bills. When the huge £31,000 estimated bill arrived Npower told Pontin to ignore it while they investigated. Read the full story here.