Microsoft is to make a public example of two UK companies accused of using its software without a licence, after hearing evidence from controversial software policing organisation the Business Software Alliance (BSA).

The main legal action has been launched in the High Court against Harrow-based teleconferencing provider ACT, alleging the 350-person company used "illegal" software on 125 of its PCs. A second action in the Central London County Court alleges that London-based legal firm Thompson & Co used unlicensed software on 23 of its PCs. In both cases, the claimed software theft relates mainly to the Microsoft Office suite.

Details of how the possible abuses came to light are sketchy, but a spokesperson for the BSA confirmed that the licence irregularities had been reported to the organisation through an unspecified channel, which investigated them on behalf of Microsoft, a member company. According to the source, the abuses would have had to have been deliberate to attract the organisation’s attention, but it is hard to verify this claim in advance of the court case.

"The BSA and its members are happy to advise and work with companies that need guidance with regard to software licensing and help them through the compliance process, so there is no excuse. Those who deliberate use illegal software and consistently refuse to comply can expect to face serious consequences," said the BSA’s Sarah Coombes in an official statement.

The contentious feature of such cases is why they come to court at all - on which the BSA is able shed no light in this instance - nor why Microsoft had become involved rather than use the BSA as its proxy. The last such UK case, from January 2006, in which a company called Prism Leisure was accused of using Microsoft and Adobe software without licence, ended in a modest out-of-court settlement of £8,000 in BSA’s favour.

"Copyright law states that each software program must have a licence, said a company spokesperson, reiterating the BSA’s hard-line approach to software enforcement. "As companies become more dependent on IT, it can become harder to manage their software assets - this is why we recommend companies deploy effective software asset management processes."

The BSA admits to receiving tip-offs from members of the public, and it looks highly likely that this was the means through which the current cases began. The organisation has a policy of paying informants up to £20,000, an incentive which has been criticised as tempting disgruntled employees to make accusations against their former employers. The BSA says it is currently investigating 100 companies in the UK.

"The BSA acts upon information supplied by the public, including reports of software piracy to its website. It's important to note that court action is always a last resort," said a BSA statement.

Whatever the legal rights and wrongs of the new actions, critics will still point to the BSA’s reporting policy as being designed to intimidate small businesses on behalf of huge, rich software houses such as Microsoft that in return offer no compensation for software failures.

The organisation publishes an interactive guide to help companies comply with best practice.