Local authorities are threatening to ditch Microsoft software unless it rethinks its costs for upgrading to XP.

Robin Carsberg, president of the Society of Information Technology Managers (SocITM), and head of technology at Braintree Council, said his is one of several local authorities evaluating alternative platforms. "We're looking at implementing Linux and possibly StarOffice 6 if it lives up to its promise," he said.

SocITM has estimated the cost of XP upgrades to local government at £80m, which is contested by Microsoft.

Carsberg said that local authorities had not been impressed by Microsoft's moves to soften the financial blow of XP. "A lot of councils are choosing to ignore what Microsoft has said. If that means we pass a deadline and have to buy differently priced versions of Windows and Office then it's better than paying our share of that £80m," he explained.

Len Graves, former president of SocITM, said: "Many local authorities are exploring alternatives and we expect to see local authority attendance at forthcoming open source events."

Local government pressure on Microsoft over XP has not been limited to the UK. SocITM has shared information with its international counterparts in an effort to gain a more effective bargaining position with the Redmond giant.

Carsberg said the co-ordinated international response of local government organisations had been significant. "Microsoft has suggested that this is a UK problem. But we have strong alliances with our colleagues in the US, Sweden, The Netherlands and New Zealand. They're 100 per cent behind us," he said.

"The reality is that when you start to talk about local government in all those countries, you're talking about a significant part of Microsoft's business. As big as Microsoft is, there will come a point where it begins to hurt," warned Carsberg.

XP licensing manager Duncan Reid said the company had discussed licensing issues with customers because it wanted to understand their concerns. "The onus is clearly on Microsoft to prove the value of its products," he added.