"We recently ruled against Number Directory Ltd t/a contactvirginmedia.com, a telephone directory website that offered a call-forwarding service, for misleadingly implying an association with a third-party telecoms company. Also, it did not make clear the advertised number was more expensive than the third party’s official customer services number.

We’ve received a steady stream of complaints on this issue and have looked at similar websites for call-forwarding services to airlines, utilities and telecoms companies, amongst others. Consumers are urged to check these websites closely before making a call.

The best way, of course, to ensure you have the official contact number is to check the company’s own website.

For marketers, the Committee of Advertising Practice (CAP) recommends that call-forwarding services should:

Make clear they provide a call-forwarding service rather than an official number for third-party services:
Rather than saying “contact x here”, claims such as “We can forward your call to x” and “We can connect you to x” are less likely to give a misleading impression.
A prominent statement making clear the nature of the service is advisable, but a disclaimer alone would not be sufficient to dispel a misleading association with a third party website, so marketers should avoid repeated references to a third party and its products, or using similar colour schemes as the third party’s corporate branding.
Call-forwarding services should also make call charges clear, in line with Ofcom's Clearer call charges, which came into force on 1 July. Please also see CAP’s advice on call charges.

If you are a consumer or marketer and are concerned about claims on a call-forwarding service website, please make a complaint via our website, which will pass the matter to the appropriate ASA or CAP team."

https://www.asa.org.uk/News-resources/Media-Centre/2015/Call-forwarding-services.aspx#.VbkDNPlViko