Whitehall spending on Directory Enquiries revealed
Some government departments are spending thousands of pounds on calling Directory Enquiries, despite the service being free online.
Every year, some call premium rate 118 directory enquiry services, but other departments have a ban on such calls.
The Department for Work and Pensions (DWP) spent more than £15,000 calling these numbers more than 10,000 times, BBC Radio 4's You and Yours discovered.
A DWP spokesman said 118 calls were only used as a "last resort".
"Staff are advised to use internet services first," he said.
"It is important for our staff to be able to contact customers, in particular the most vulnerable, to make sure they are getting the support they need."
You and Yours also found that HM Revenue and Customs spent £12,065 last year, and £26,753 over the past three years making 43,552 calls.
A spokesman for the tax authority said 118 numbers had now been barred and staff were only permitted to use a special low-cost corporate directory enquiry service as a last resort.
The Passport Office spent £19,132 over the past three years calling the services more than 5,000 times, You and Yours also discovered. In some cases it cost as much as £54 a call as staff stayed connected for more than 30 minutes.
The department said that in a tiny proportion of cases staff needed to use directory enquiries to verify information and "support the processing of applications".
The research found different policies in place across government departments. The Department for Communities and Local Government (DCLG) and the Home Office ban all calls to 118 services, as has the Department for Education since 2014.
These 118 services provide access to phone numbers at a premium rate call charge. Some services allow the caller to be connected directly to the number, but continue to pay the premium rate.
A call to BT's corporate 118 707 service used by many of the government departments costs 29p per call and will not connect a caller.
Calls to BT's international directory enquiries number, 118 505, cost £1.90 per call then £3.84 per minute - which continues to be charged if the call is connected through.
For UK numbers, BT's Phonebook is available to search online free of charge. There are also free online international directory enquiry services.