A trader cannot charge more than a basic rate for telephone help-lines. A consumer cannot be made to pay more than the basic rate for that call (regulation 41(1), Consumer Contracts Regulations).
There is an argument that 10 pence for landline is a basic rate as there is no definition of basic rate in the Consumer Contracts Regulations. According to the BIS Guidance (page 20), the basic rate is no more than a geographic or mobile rate.
If you feel you have been charged by a trader or know of a trader who charges too much for their phone line then the Trader must reimburse payment to consumer (regulation 40(4), Consumer Contracts Regulations) and if not you have two options
1. Sue in the small claims court or 2. Report them to Trading Standards
Let me know if you are aware of a trader who charges for a phone call! Write to them – they will soon stop if more of you complain!