The battle to sign up players for the multi-user cult adventure MUD doesn't officially begin until later this month, when British Telecom's upgraded version is launched in opposition to the established Compunet game.

But there has already been one "error induced" skirmish, and both competitors are claiming to offer the best value for money.

The BT New Information Services version, rewritten by Roy Trubshaw and Richard Bartle to incorporate more locations and new languages, will be offered free during a trial period between September 8 and November 5.

The MUD Pack containing the necessary documentation, ID and initial credits will cost £20. "From November", says Mike Anderiesz of New Information Services, "it should cost the average player about £2 an hour plus the cost of the telephone, which can be as low as 40p an hour if the player lives in the London area".

By buying credits in blocks of 1,500 for £150, players can bring their costs down to £1 an hour, says Anderiesz.

To counter the opposition from BT, Compunet is offering £3 ad hoc entry to MUD and charging £10 for an introductory six hour period. After that players get a choice of three different rates - £5 a month plus £2.50 an hour, £ 15 a month and £2 an hour, or £25 a month and £1.75 an hour.

Play is charged by the half minute, whereas BT's credits come in units of 20 seconds.

Compunet's jane Firbank claimed victory regarding costs. "We have 12 access nodes around the country to enable people to play at local call rates as low as 40p an hour. The other version has only one number available, in London, so callers from outside areas will find themselves facing very steep charges".

Anderiesz countered: "Compunet's rates are excluding VAT while ours are VAT inclusive. I believe our version is the more economical in the long run, apart from being more sophisticated".

There was consternation at BT New Information Services and at Multi User Entertainments - owner of the rights to MUD and its development languages - over a recent issue of Compunet News edited by Jane Firbank.

It stated: "MUD is now available to those who are not members of Compunet. Anyone with a home micro and an ordinary 1200/75 baud modem can now play Compunet's MUD, often at local call rates through one of Compunet's 12 access points nationwide".

Officials at BT complained that this was an apparent breach of Compunet's agreement - confirmed by Muse managing director Simon Dally - not to promote MUD outside Compunet, and an infringement of BT's exclusive right to offer the game to the general public.

But the problem was smoothed over when Compunet boss Alan Carmichael assured Muse that all players of MUD on Compunet would have to register as associate members if they were not full subscribers, and have an official ID.

Dally, partner in Muse of Trubshaw and Bartle, told TeleLink: "We have been advised of an error in the Compunet announcement concerning the availability of MUD outside that network. We have been assured that this version of the game will only be available within the Compunet service in accordance with our existing agreement".

Meanwhile Dally has revealed that Muse is having "serious discussions with leading US companies which I'm confident will result in agreements regarding MUD being signed in the near future".

Strangely, Dally reports: "We haven't discovered anybody in Europe who is interested in the game so far".