I'm not a conservative but .....
..... I think Microsoft would be worse than a Conservative government.
Widespread adoption of Open Source Software will put an end to IT projects haemorrhaging money to Microsoft, and instead create jobs in the UK. That isn't going to be nearly as expensive in the long term as it looks. Adapting Open Source Software to suit the UK public sector -- and dealing with the baggage left behind by years of using closed-source software with undocumented file formats -- may have a large initial cost, but we shouldn't forget that the work will be done by local programmers. Local people buy goods in local shops, pay local taxes, eat in local restaurants, donate to local good causes and take their families to visit local tourist attractions. In other words, the money that you pay them stays in the local economy. And the benefits of their improvements to existing Open Source Software will be available to everyone.
Contrast this with the quick-fix solution offered by Microsoft. You have to pay for every copy of client software. You have to pay more for server software depending how fast a machine it runs on and how many people are using it (creating the riduculous situation where a company can find it economically preferable to turn away business rather than take on additional staff, because taking on additional staff would mean having to upgrade their software and they can't afford to do that). And if the software disrupts your existing workflow, tuff titty! You can't adapt it to suit your needs, you just have to work the way the software expects. And a couple of years down the line, the software will invariably have to be upgraded to a new version -- which, of course, costs money. That money goes out of the local economy forever, and just makes multi-billionaires even richer.
By the way, if the Conservatives included in their manifesto a promise to make it illegal to conceal the Source Code of *any* program from its users, then I'd vote for them in a heartbeat.