In the meantime the only sensible policy is not to do business with any company which uses these Disguised Premium Line (DPL) numbers. There are still honest and straighforward companies which do not play these tricks to increase their profitability, and don't make you pay for sorting out any mistakes which they have made because you have to telephone them to tell them on one of these DPL numbers.
Oftel is of course soon to be dissolved and a new body will take over the responsibility for regulation. It seems that since BT saw these numbers as being an opportunity to claw-back some of the monopoly which they had lost, they have now also begun to actively sell the DPL concept to companies via agents pushing the idea that companies can generate considerable revenue from their customers if they change their numbers (particularly call centres) to these DPLs. OFTEL has begun to address this scam with 07 prefix numbers by BT, but have so far evidently taken no action about the scam of 04, 05 and 08 prefixes in being used as DPLs.

The address of OFTEL is: 50, Ludgate Hill, London, EC4M 7JJ.

I suggest that consumers angered by this scam should write to OFTEL, OFCOM, ICSTIS and their own MP to complain. The address of OFCOM is: Riverside House, 2A Southwark Bridge Road, London, SE1 9HA.
The address of ICSTIS is: Freepost, WC 5468, London, SE1 2BR.

It seems that The Consumer's Assocation is now beginning to look at this SCAM.

Thanks, I'd be interested to hear about some examples of rip-off 04 and 05 prefixed numbers, which you mention.

The only in-use prefix of these ranges that I'm aware of is 0500 (no fee); e.g. code 0541 is long since deprecated, isn't it?

Oops!  I just replied to the original thread started by RD!  Just noticed this second thread, D'oh!  How comes you continued your orignal post using another thread anyhow? ::)  :)