I have been with Virgin for years and didn't know about this free service. Found out whilst reading on their booklets they sent me.
BT Directory Enquiries costs £1.99/ min plus connection fee of 62p
Probably going to go stone cold but hopefully it will help someone.
Free Calls to Virgin Media National Directory Enquires (118 180): Free Calls to Virgin Media National Directory Enquiries Service on 118180 are only available from a Virgin Media Home Phone (cable & national) and Virgin Mobile and are included within your tariff; charges apply for calls to 118180 from other operators. Fair Use Policy applies with a maximum of 10 calls per day. You are responsible for making sure that you do not exceed this allowance. If you do exceed the allowance, we reserve the right (at our sole discretion) to charge you for the call (30p per call). Onward connection restrictions apply.