The UK's telecoms watchdog is firming up plans to investigate the directory enquiries market.
Yesterday, the soaring cost of phoning services to find out a telephone number was revealed.
Operator 118 118, famed for its TV campaign featuring a moustached running duo, recently upped its minimum price to £8.98. Ofcom has warned other firms charge up to £10.50 for one call.
A spokesperson for Ofcom said: "Ofcom is very concerned about the rising prices of some 118 numbers, and we are already planning to review this market to ensure prices are transparent and fair to consumers. We will announce further details soon.”
The precise timing of the regulator's plans are yet to be firmed up, however it is understood that more details will be provided in days rather than weeks.
The directory enquiries sector is dominated by four players. Alongside BT and 118 118 are Yell (118 247) and Maureen (118 212), which have minimum charges of £5.50 and £6.98 respectively.
Competition in the sector was introduced in 2003, when it cost 40p to dial BT's 192 directory enquiries service.
118 118 is the trading name for The Number UK Limited, which is owned by US privately-owned firm Knowledge Generation Bureau (KGB).
The firm also owns UK mobile search service Texperts and set up its own version of 118 118 in the US in 2009. In 2013 it was ordered to pay $1.3m by the US labour department to some of its internet researchers, which it concluded had been underpaid.