Could open source help the UK government cut its carbon emmisions?

The BBC are reporting that Computer systems generate up to 20% of all carbon produced by government, and that the UK government is going to have a carbon neutral IT system within 4 years. I wonder if they have considered cutting their electricity usage by using open source?

I noted sometime ago from Alan Lord (when writing our corporate social responsibility statement) that Linux is alleged to use less power than conventional Windows platforms. I am very out of touch with current thinking on this issue, but just thought I’d flag this up.