On theri website RS Components give an 0845 number for most contacts. There's a perfectly good 01536 number listed on SayNo and it's on some of their documentation.

So far so good.

They present themsleves as a b2b company and don't like dealing with individual consumers. I have an account with them and am therefore definitely a business customer.

Are they required to give the calling costs for their 0845 numbers?

Where a telecoms company offers telephone service to retail customers they must charge calls to 084, 087, 09 and 118 numbers as Access Charge plus Service Charge.

Where a telecoms company offers telephone service to business customers they have the choice of charging as Access Charge plus Service Charge, flat-rate pricing or some other scheme.

Given that some callers calling RS will be subject to Access Charge plus Service Charge pricing why would RS seek to withhold a vital piece of call charge information that those callers will need?

RS has either misunderstood or is in denial about the true nature of the call charges for their 0845 numbers:
www.nidirect.gov.uk/the-cost-of-contacting-08-and-03-telephone-numbers