Britain's Entertainment Retailers Association is turning the screw in its crusade against "covermounting."

The trade body has sent a letter to British magazines and newspapers authority ABC, bringing into question the Mail on Sunday's giveaway of the Prince album "Planet Earth" this weekend.

ERA accuses the national newspaper of hyping its circulation figures by offering the 10-track CD free as an incentive to purchase.

"We believe that this promotion and others like it potentially distort the accuracy of ABC's audit in a way which could mislead advertisers and others using of your data," ERA writes.

As previously reported, Sony BMG in the United Kingdom has refused to handle the release of the album in light of the newspaper giveway. ERA argues that the CD would have carried a retail value of between £8 ($16) and £10 ($20), roughly seven-times the £1.40 ($2.80) cover price of the publication.

"The inescapable conclusion must be that this is a blatant attempt by the MoS to skew its circulation figures," ERA writes.

It continues, "We believe that if ABC allows such 'hyping' of a newspaper's circulation figures by the use of excessive incentives it can only undermine the currency of an ABC audit and ultimately undermine your greatest asset, your credibility."

ERA concludes, "It is entirely possible that 10s perhaps 100s of thousands of copies of this Sunday's MoS will be purchased solely so that readers can get their hands on 'Planet Earth' and that the newspapers themselves are cast unread. It would be very wrong for such copies to count towards the Mail on Sunday's ABC audit. We request you urgently to investigate the Mail on Sunday's promotion and we urge you strongly to disallow sales made on the basis of disproportionate incentives."

It is unlikely, however, that the ABC will make any such investigation. In a note issued this afternoon, the organization explained that giveaways were allowed as an incentive to buy newspapers. "Reader incentives have been a feature of newspaper sales for many years. More recently these have included CDs and DVDs," the group explains.

The Mail on Sunday newspaper was at the heart of an earlier row following the distribution of Mike Oldfield's 1973 seminal prog-rock work "Tubular Bells".

Some three million copies were pressed up for that CD, and a similar number of "Planet Earth" discs are expected to have been manufactured. The Mail on Sunday has a current audited figure of 2.27 million.

When asked how many copies would be made, Stephen Miron, the managing director of the Mail On Sunday, recently told "This is all into the unknown, but I think we're going to sell out whatever we print at the moment.

He added, "Now that Sony BMG has pulled the launch of the album, the only available mechanism to get this new album is with the Mail on Sunday. I would say £1.40 for the album is probably good value. Unfortunately, a lot of people will buy to sell, because obviously on the international market, people will look at this as an opportunity to exploit through eBay. From our perspective, we're not doing it for that reason. It's another unique promotion for the Mail on Sunday."

Earlier this week, HMV came under attack from its rival High Street retailer Virgin when it struck an agreement to distribute copies of the Sunday newspaper in its outlets.

Copies of Prince's new record have also been given-away to ticketholders for Prince's 21-date residency at London's O2 Arena.