Ofcom have offered many different versions of the necessary call cost statement for 03 numbers. The phrase "national rate" has been used. In theory, telecos could charge different rates for national and local calls, although they generally do not.
The latest version of the Ofcom statement, found in the current version of
“Number Crunching” should be fine for most purposes:
Quote:Calls cost no more than calls to geographic numbers (01 or 02) and must be included in inclusive minutes and
discount schemes in the same way.
(N.B. Although the URL implies January 2010, the 'Number Crunching' document is subject to regular updates.)