For the sake of completeness, the below is the e-mail response I got from Ofcom (typical quango 'non-reply' IMHO).
11 Aug 2004
Dear Mr Heinz
Thank you for your email to Ofcom. In this you complained about the misleading use of the term “National” rate for calls to non-geographic 0870 numbers, now that BT has reduced the cost of calls to national geographic numbers following its BT Together price changes.
By way of background, I should explain that 0845/0870 numbers are known as Number Translation Services (NTS) ie the non-geographic number sits on top of a geographic number. The NTS regime was created to encourage the provision of innovative value added services by terminating operators and service providers.
Ofcom is aware of consumer concerns that they might be misled on the promotion and marketing of both 0845 and 0870 numbers and we also share concern about their proliferation. On 29 April 2004, Ofcom issued a statement and announced a further consultation on 0845/0870 retail pricing. Following this we are now actively working with advertising regulators and consumer bodies to agree how the prices for these calls should be advertised. We are also re-examining the way in which the entire NTS regime operates and will be consulting widely on our proposals in the early autumn. One of the possible options could be to require originating providers to provide price warnings of the prices of NTS calls before connecting the call but we have not finalised any views yet.
If you wanted to see a copy of the Ofcom statement and further consultation it can be found at
http://www.ofcom.org.uk/consultations/past/0845/?a=87101 which is also where any further consultations will be published.
Yours sincerely
Steven Parker
Ofcom Contact Centre